Great Lakes Rivermouth Ecosystems
An Agenda for Science and Management

Contents

I.      Introduction.3

A.        The Need for a Rivermouth Agenda.3

B.        What is a Great Lakes Rivermouth?.3

II.    Rivermouth Ecosystem Services, Alterations and Values.3

A.        Ecosystem Services.3

1.         Provisioning Services.3

2.         Regulating services.3

3.         Cultural services.3

4.         Supporting services.3

B.        Human alteration of rivermouth ecosystems.3

1.         Eutrophication and Chemical Pollution.3

2.         Hydrologic and Physical Alteration.3

3.         Invasive species.3

C.        Putting an Economic Value on Rivermouth Ecosystem Services.3

III.      Rivermouth Science: What do we know?.3

A.        Conceptual Model of the Rivermouth.3

B.        Physical Processes and Setting.3

1.         The upstream watershed (the river)3

2.         The associated Great Lake.3

3.         Local setting.3

4.         Human Alterations.3

C.        Chemical Processes.3

1.         Chemical Aspects of nutrients/contaminants loading from river/watershed and Great Lake.3

2.         Different Micro-habitat processing environments:3

3.         Chemical gradients:3

D.        Biological Processes.3

E.         Science and Research Needs.3

1.         Physical:3

2.         Chemical:3

3.         Biological:3

IV.      Rivermouth Conservation and Management3

A.        Roles and Responsibilities.3

B.        Watershed Scale Conservation Programs.3

1.         Watershed management3

2.         Nonpoint source control3

3.         Coastal management_____.3

4.         Climate Change ___.3

5.         Other??__.3

C.        Local Conservation and Management Programs and Activities.3

1.         Land Use management3

2.         Wetland conservation.3

3.         NPDES/point source control3

4.         Habitat and Special Area management (parks, beaches, etc)3

5.         Ongoing Human/Societal Uses (specific programs to mitigate their impacts)3

6.         Other?)3

D.        Management Needs.3

1.         Monitoring and Evaluation.3

2.         Implementation.3

3.         Prioritizing protection and restoration/decision support tools -.3

4.         Promote a Systems approach.3

5.         Link science and restoration to economic growth, sustainability and quality of life.3

6.         Public Policy to support rivermouth conservation.3

7.         Advocacy/Education and outreach.3

V.    Creating A Rivermouth Collaboratory-"How to Make it Happen".3

A.        Coordinating and Implementing Rivermouth Science, Management, and Policy.3

B.        Sustaining the collaboratory.3

C.        Coordinative Science Forums.3

e.g. social media, other information-sharing mechanisms etc.3

VI.      Literature Cited.3

 

 

I.     Introduction

A.    The Need for a Rivermouth Agenda

Great Lakes rivermouth ecosystems are regional centers of human activity and biological production and diversity.  These systems provide a range of important services that benefit the Great Lakes region directly and indirectly, and are the places where inland and supporting riverine communities and ecosystems connect to the Great Lakes.  Despite their importance, the study and management of rivermouth ecosystems has been minimal and piecemeal, focused on a few individual systems or on particular features or types of rivermouth ecosystems.  The success of current and long-term efforts to restore and effectively manage rivermouths requires understanding how they function as systems, especially in the face of transforming nearshore economies and climate-induced changes in river flows, water levels, and lake storm patterns.

Rivermouths are the location of complex interactions between riverine and Great Lakes processes.  The researchers who study these different ecosystems are fragmented among agencies and institutions that often work independently, and utlize communication mechanisms that are often similarly disparate.  Furthermore, little coordination occurs between organizations that manage various aspects of rivermouth systems. Ecological restoration and long-term sustainability of rivermouths requires improved scientific understanding and synthesis of the structure and function of these ecosystems, and a holistic set of strategies and priorities.

This Great Lakes Rivermouth Agenda (Agenda) summarizes the current scientific understanding of these unique ecological systems as a distinct group, identifies key gaps in our scientific understanding, and presents a framework for institutions to collaborate over the long term to restore and preserve the valuable services provided by these ecosystems.  The Agenda proposes a list of activities needed to better understand and manage the ecological function of rivermouth systems and a plan for implementing these activities, thereby providing a critical link between management and scientific research in tributaries, coastal wetlands, embayments, and coastal waters of the Great Lakes. 

B.     What is a Great Lakes Rivermouth?

Rivermouth areas in the Great Lakes can be thought of as freshwater analogs to marine estuaries -biologically productive areas that support high biodiversity and provide habitats critical to the life-cycle and productivity of many species (cf. McLain et al. 2003).  As in marine estuaries, several elements of rivermouths contribute to this status: 1) extended water residence times, which allow for enhanced biogeochemical cycling; 2) generally shallow bathymetries, which allow for development of structurally complex and often well-vegetated littoral habitats; and 3) high diversity of physical and chemical conditions within limited space, which supports a diversity of organisms. (Section II provides a detailed description of Great Lakes Rivermouth systems.)  Also in common with marine estuaries, humans have exerted substantial pressures on Great Lakes rivermouths.  Rivermouths and estuaries are often centers for human settlement, because they offer offer natural harbors and nexuses for travel and commerce, as well as valuable recreation opportunities including fishing, hunting, birding, and beaching.

II.  Rivermouth Ecosystem Services, Alterations and Values

A.    Ecosystem Services

We believe that Great Lakes rivermouths may be among the most important of all Great Lakes environments, as they provide many critical ecosystem functions and services.  This contention is based on indirect evidence, as there is a virtual absence of literature that specifically addresses rivermouths.  Instead, considerable literature documents the importance of Great Lakes coastal wetlands, embayments, and lower tributary reaches (Jude and Pappas 1992, Albert and Minc 2004, Wei et al. 2004, Niemi et al. 2007, Ogdahl et al. 2010, Sierszen et al. 2011).  This related literature has been extended where appropriate to discuss the ecosystem services provided, either presently or historically, by rivermouth systems.

Ecosystem services can be defined in a number of ways, each with some strengths and weaknesses (Costanza et al. 1997, Daily et al. 1997). We have followed here the framework adopted by the Millennium Ecosystem Assessment (2003) to categorize ecosystem services.  However, it is important to keep in mind that these services are linked among these categories as well.

1.     Provisioning Services[G.L.C.1] 

Provisioning services are the products that are obtained from ecosystems, including food and fresh water.  Great Lakes rivermouths provide valuable habitat for life stages of some of the fish that support a multi-billion dollar fisheries industry[G.L.C.2] .  Rivermouths are nutrient rich with respect to the nearshore and offshore areas of the Great Lakes (Biddanda and Cotner 2002) and many Great Lakes fishes migrate to rivermouth systems for feeding, spawning, rearing and protection from predators (Schlosser 1991, Jude and Pappas 1992, Wei et al. 2004).  This fishery support function is analogous to that provided to marine species by saltwater estuaries (e.g., Barbier et al. 2011, Engle 2011).  For example, adult lake sturgeon use drowned river mouth lakes as staging areas before initiating spawning runs in some Great Lakes tributaries, and juveniles use these systems as nursery habitats for months to years before entering the Great Lakes (Altenritter 2010). Coastal wetlands (which in many cases are at rivermouths) are thought to be used by 75-90% of Great Lakes fish species during at least part of their life cycle (Jude and Papas 1992, Brazner et al. 2000, Höök et al 2008, Sierszen et al. 2011).   Even plumes of turbid river waters can serve to shelter small fish from visual predators in the near-shore Great Lake environment (Reichert et al. 2010).

Rivermouths not only contain high-quality habitat used by fishes, but also by birds, amphibians, reptiles, and other wildlife (e.g., Riffel et al. 2001, Hecnar 2004, Howe et al. 2007).  Rivermouths have substantial animal productivity and biodiversity (Mitsch and Gosselink 2007, Wilcox and Xie 2008, Bouvier et al. 2009).  These habitats are also important for regional biodiversity as they seem to be less readily colonized by some invasive species, such as round goby and dreissenids (Cooper et al. 2007, 2009, Nelson et al. 2009). 

2.     Regulating[G.L.C.3]  services

Regulating services are the benefits obtained from the regulation of ecosystem process, such as erosion control, flood protection, water levels, transportation, and other ecosystem processes.  The facilitation of boating has long been a critically important service provided by rivermouths.  Rivermouths provide natural harbors from storms and high wave-action, and as a result many Great Lakes urban centers grew from industrial port communities located at rivermouths.  The importance of marine estuaries in this regard has been fairly well documented (e.g., Engle 2011, Barbier et al. 2011), but little work has documented this in the Great Lakes (e.g., Silander and Hall 1997).  In addition to commercial shipping, rivermouths provide protection for recreational boating and thus access to the Great Lakes for tourism.

Many rivermouth ecosystems include depositional areas and wetlands that serve as both flood-storage reservoirs and areas that trap sediments.  As a result, these areas reduce the sediment entering shipping channels, reduce turbidity and lead to overall improvements in water quality.  Where not degraded, high water quality (i.e., few pollutants, low turbidity) in turn generally reduces the likelihood of harmful algal blooms and contamination of provisioned services (e.g., fish), while increasing the value of associated cultural services (e.g., ecotourism). 

As with many aquatic ecosystems, rivermouth ecosystems have also historically been valuable for their ability to remove, breakdown or even sequester excess waste nutrients or xenic compounds (Costanza et al. 1997, Postel and Carpenter 1997).  However, the capacity of humans to generate waste has often greatly exceeded the ability of these (or other) ecosystems to effectively perform this service without severely damaging other important ecosystem services.  Similarly, many power plants and other industries use rivermouth and Great Lakes water to dissipate waste heat (i.e., provide cooling; Postel and Carpenter 1997).

3.     Cultural services

Cultural services are the non-material benefits people obtain from ecosystems through enrichment, recreation, and other aesthetic experiences.  These services are often difficult to quantify, but include tourism, recreational fishing and boating, and increases in the value of nearby habitats. In addition to the benefits associated with recreational fishing and boating (described above), the Great Lakes attracts a diverse array of tourists that sustains many coastal communities during summer months.  Millions of visitors annually visit the parks, natural areas, and trails that provide access to rivers, rivermouths and the Great Lakes shorelines. These areas are managed to provide public access and provide a way for residents and visitors to experience and interact with the natural environment. An ecosystem service valuation study of land uses associated with green infrastructure revealed that real estate along west Michigan lakeshores were associated with the highest values (Isely et al. 2010), indicating its socio-economic importance.  Another analysis revealed that a $10 million (USD) shoreline restoration and habitat restoration project in Muskegon Lake, a Great Lakes Area of Concern, will result in more than a 6-fold return on investment because of increased property values, new tax revenue, and additional recreational spending (P. Isely, unpubl. data).

4.     Supporting services

Supporting services are those that are required for the other types of services an ecosystem provides. Essentially they are the indirect and occasionally long-term support mechanisms that allow ecosystems to provide the short-term benefits that have direct economic benefits.  Many services can be categorized as both supporting and some other type of service.  For instance, the ability of rivermouth depositional areas to remove sediment is a regulatory service because it directly benefits activities associated with ship passage by reducing sedimentation in shipping channels. However, these depositional areas also support the provisioning of fish production in the Great Lakes by helping to maintain water quality within the range of conditions that promote fish growth and reproduction.

Rivers often carry substantial loads of carbon, nitrogen, and phosphorus that support and shape near-shore and offshore Great Lakes food webs (Bouchard 2007, Johengen et al. 2008).  However, naturally functioning rivermouth ecosystems are also thought to act as a filter for nutrients and sediments coming off the landscape (Klarer and Millie 1989, Mitsch and Gosselink 2000, Krieger 2003, Wilson et al. 2005), which can be especially high in agricultural or urbanized watersheds.  As in marine estuaries (e.g. Smith et al. 1985), rivermouth ecosystems have a large capacity for reducing nitrogen through both denitrification, whereby nitrate is reduced to nitrogen gas and lost to the atmosphere, and assimilation into plant material (Tomaszek et al. 1997).  External phosphorus loading to the Great Lakes likely is reduced by biogeochemical processing within rivermouth zones (Krieger 2003), although internal cycling complicates matters (Steinman et al. 2009), as do water-level fluctuations.  These energy flows from river to lake also occur in the reverse, when adfluvial fishes return from the lake to spawn in rivers and rivermouth zones (Flecker et al. 2010, Lamberti et al. 2010). 

B.     Human alteration of rivermouth ecosystems

Rivermouth ecosystems have long been a focal point of anthropogenic impacts in the Great Lakes region due to the many services they provide, the many human activities they support, and the rich agricultural landscapes they drain.  Riseng et al. (2010) and Mackey (2009) have noted that nearshore and coastal margin areas are not only the most dynamic and diverse biological areas in the Great Lakes, but are also the locations where humans interact with the Great Lakes. In association with urban settings, humans have generally managed rivermouths to maximize their utility as providers of shipping, waste disposal and flood protection.  Other ecosystem services have suffered substantial impairments as a result. The Area of Concern (AOC) designation is used across the Great Lakes to indicate ecosystems with substantial ecological impairments:  most AOCs are rivermouth ecosystems.
The use of aquatic ecosystems for waste disposal represents a substantial benefit to many industrial activities (Daily et al. 1997).  However, chemical pollution and nutrient enrichment due to intense urbanization, agriculture and industrialization has resulted in heavy impacts to rivermouths and their associated embayments and coastal wetlands (Krieger et al. 1992, Steinman et al. 2006, 2008).  Chemical pollutants degrade the ability of aquatic ecosystems to support a diverse and productive biotic community (Reynoldson and Zarull 1989, Schloesser et al. 1995), reduce the recreational value of an ecosystem (IJC 2009) and may overwhelm existing biogeochemical cycles (Steinman and Ogdahl in press).  Effects of inputs of nutrients resulting from agricultural activities in the watershed, have been well studied in the Great Lakes, as they have in many other aquatic ecosystems (e.g., Carpenter et al. 1998, Howarth et al. 2000).  Details of the eutrophication response depend on the primary producer and consumer communities present as well as other physical and ecological constraints, but the general effect is that increased nutrients stimulate algal production.  When the stimulation is in the water column (i.e., planktonic), benthic algae and submerged vegetation growth can be suppressed via shading, ultimately affecting faunal production and composition via a combination of habitat-mediated and food-web mediated pathways (Hansson 1992, Vadeboncoeur et al. 2003, Chow-Fraser 2007, Trebitz et al. 2009a).  However, nutrient runoff can also stimulate benthic algal production (e.g., Cladophora), which can lead to both ecological impacts through food web interactions as well as economic impacts associated with water intake clogging and links to human pathogens (Higgins et al. 2008, Auer et al. 2010).

2.     Hydrologic and Physical Alteration

Manipulation of estuarine floodplains for either flood protection (e.g., Smits and Nienhuis 2006) or water retention (e.g., Becker and Laurenson 2008) often leads to dramatic changes in biotic communities, sedimentation patterns and other structural properties.  Even relatively small developments within rivermouths and their riparian environment can have substantial effects on structure in these ecosystems (Trebitz et al. 2005).  Although many of these developments have improved the utility of rivermouths for shipping, flood abatement, and recreational boating, the loss of temporal and spatial habitat complexity has reduce the ability of rivermouths to provide habitat for fish and wildlife and conditions conducive to nutrient processing (XXX). [G.L.C.4] In particular, shoreline and bathymetric modifications resulting from dredging and installation of breakwalls, levees, roadways, etc. have drastically reduced the availability of high-quality littoral habitat, both through forced disconnection of formerly connected areas (backwaters, etc.) and through direct or indirect destruction of aquatic and emergent vegetation beds (Jude et al. 2005, Steinman et al. 2008). 

3.     Invasive species

As a focal point of transportation, shipping and human settlement, Great Lakes rivermouths have been subject to the intentional and unintentional introduction of non-native species (Mills et al. 1993).  Many of the non-native species have become established, and now have heavy impacts on a wide variety of ecosystem services provided by the Great Lakes in general and rivermouths in particular (Ricciardi and MacIsaac 2000, Jude 2001, Pimental 2005; XXX[G.L.C.5] ).  A few of these non-native species have become important economically as replacements for lost native species (e.g., Pacific salmon species; alewives). The impending threat of an Asian carp invasion has particular relevance for rivermouths, as these systems may be the only ones in Lakes Michigan, Huron, and Superior with sufficient plankton resources to sustain them (Cooke and Hill 2010), assuming they enter the Great Lakes.

C.   Putting an Economic Value on Rivermouth Ecosystem Services

We are not aware of any estimates of the comprehensive economic value of Great Lakes rivermouths, but such an estimate would be useful.  Recognition is needed that the alterations to Great Lakes rivermouths have resulted in a variety of often contrasting economic impacts.  Increased navigation, commerce, and infrastructure have resulted in substantial economic development that can be valued through traditional markets. However, there has been a concomitant loss of the benefits that these natural ecosystems provide to humans (Millennium Ecosystem Assessment 2003). Because these ecosystem services rarely pass through traditional markets, they are largely unrecorded (Heal 2000; Daily et al. 2009). The value of many of these ecosystem services has not been well-quantified because of the limitations inherent in the application of these traditional valuation techniques to nonmarket goods and services.

Although ecosystem service valuation studies have not been conducted specifically for Great Lakes rivermouths, Isely et al. (2010) used a benefit transfer approach to value wetlands in the west Michigan region at $81,483,097.  Whitehead et al. (2009) found the total present value of coastal marsh in Saginaw Bay could reach $2421/acre.  Braden et al. (2009a,b) estimated the economic benefits of remediation in two Great Lakes AOCs; they found that single-family residential property values were depressed by $118 million in the Buffalo River AOC and $158 million in the Sheboygan River AOC.  In a more holistic analysis of Great Lakes restoration, Austin et al. (2007) reported that a present-value total investment of $26 billion in ecological restoration would result in over $50 billion in long-term benefits to the national economy; and between $30 and $50 billion in short term benefits to the regional economy.  The valuation of ecosystem services is particularly relevant for the Great Lakes region given the economic implications associated with invasive species (Pimental 2005) and water availability (Steinman et al. 2011).  Pimentel (2005) estimated that invasive species account for a total loss of ~$5.7 billion dollars per year. 

III.          Rivermouth Science:  What do we know?

A.    Conceptual Model of the Rivermouth

Rivermouth ecosystems are complex and diverse. Although little research has specifically focused on Great Lakes rivermouth ecosystems, a significant body of research has been developed for Great Lakes coastal wetlands.  Many Great Lakes rivermouths are also classified as coastal wetlands, and so information derived from the Great Lakes coastal wetland literature, as well as information from marine estuaries, can be used to create a conceptual model of Great Lakes rivermouth ecosystems (Figure 1), to help visualize how rivermouth ecosystems are structured and how they function. The conceptual model provides a starting point for looking at rivermouths as a distinct ecosystem and allows us to see what these systems have in common.

Controls over the biophysical structure of the rivermouth ecosystem occur at both regional and local spatial scales.  Rivermouths are areas of hydrologic mixing of riverine inputs derived from the upstream watershed and seiche/storm/wind-driven inputs derived from an associated lake or sea (Figure 1).  Rivermouths can be broken longitudinally into zones including the lower river valley (that final portion where valley slope is very low, much river sediment is deposited, and strong lake seiches have some up-river influence), a depositional area where the river channel empties into a lacustrine receiving area (this may be a drowned rivermouth lake, an embayment, or the adjacent Great Lake proper) and an offshore plume that is influenced by material exiting the rivermouth zone (dynamic both temporally and spatially). We use dashed lines to suggest that these boundaries can vary dramatically in space and time (Figure 3).  Rivermouths also vary in their lateral and vertical dimensions.  The lower river valley tends to be fairly channelized but sometimes has associated backwater habitats and floodplains, while the depositional area can be extremely wide, and include extensive emergent wetland or shallow lake-like areas that bear little resemblance to a constrained channel. Depending on the width of the opening where the rivermouth water actually enters into the adjacent Great Lake and the bathymetry and human alteration of the lakebed (e.g. dredging), the plume can be quite wide or quite narrow, represent a sharp or a diffuse boundary among water masses, and be directed out into the lake across increasing depth contours or be directed along shore by lake currents and long-shore thermal gradients.  Unlike marine estuaries, Great Lakes rivermouths do not have a salinity gradient, but do often exhibit gradients in water temperature, clarity, and chemistry.

Figure 3. Conceptual model of an idealized rivermouth system. Conceptual models are useful for visualizing systems and understanding how they work, and they promote critical thinking and scientific exploration aimed at improving the model.  This model will provide a language for scientists and managers to think and talk about system status, impairment, and potential management approaches. 

 

B.       Physical Processes and Setting

Physical processes, especially related to hydrology and geomorphology, have strong influences on both chemical and biological processes (Trebitz et al. 2009a, Trebitz et al. 2009b). Hydrogeomorphic processes also affect the mixing of lake and tributary water, which in turn, influence water quality (e.g., nutrients, turbidity, temperature[G.L.C.6] ).  All rivermouth systems are structured by three fundamental components:  the upstream watershed and river, the associated Great Lake and its subregion, and the local geomorphic conditions.  Here, we have broken up the important drivers by these fundamental drivers.. 

1.     The upstream watershed (the river)

Flow regime has an overwhelming influence on ecosystem structure and function in streams and rivers (Richter et al. 1996, Poff et al. 1997), and is likely to have similarly strong effects within rivermouths (Loneragan 1999).  Trebitz et al. (2009a) notes the importance of tributary influence in creating habitat diversity:  "Strong lake influence tends to homogenize vegetation and water quality among locations within wetlands, whereas strong tributary influence tends to foster differences in vegetation and water quality between on- and off-channel areas."  Within Great Lakes coastal wetlands, the relative importance of tributary material and nutrient inputs are controlled in part by the discharge (Trebitz et al. 2002, Trebitz et al. 2005), similar to what occurs in marine estuaries (e.g., Rabalais et al. 1998), with differential sediment delivery and deposition during baseflow and storm event periods.  Not only do rivers entering the Great Lakes span a large gradient in watershed size and thus in typical baseflow, but their flow regime varies from very flashy to very stable (Richards 1990, Detenbeck et al. 2006, Johnston and Shmagin 2008).

Natural differences in watershed physical properties (e.g., soil characteristics), geomorphology (e.g., slope, drainage density) and processes at large scales (e.g., climate, ecoregion) are known to significantly affect the chemical, physical and biotic composition of adjacent or receiving waters (Aitkenhead-Peterson et al. 2003, Frost et al. 2006, Brazner et al., 2007, DeCatanzaro and Chow-Fraser 2011, Seelbach et al. 2011). Mechanistically, these effects are driven in part by the flow paths of water and thermal environment of these aquatic ecosystems (Poff et al. 1997, Baker et al. 2003, Wehrly et al. 2006, Wiley et al. 2010).

Changing land cover and land use in upstream watersheds is known to also significantly affect the physical and chemical characteristics of aquatic water bodies (Poff et al. 1997, Johnson et al. 1997, Tomer et al. 2008, Renwick et al. 2006, Chen and Driscoll 2009, Zhou et al. 2010).  Additionally, watershed landuse can affect river flow regimes, with conversions of forested land to agricultural and urban landuse tending to increase flashiness of stream flows (Verry 1986, Richards 1990, Fitzpatrick et al. 1999) which can impact the physical, chemical and biological function of rivermouths.

2.     The associated Great Lake

Lake water movement into the rivermouth zone is primarily driven by lake currents created by typical wind regimes (Belesky et al. 1999, Kerfoot et al. 2008) and by seiches and storm surges (Bedford 1992, Keough et al. 1999, Trebitz 2006).  Seiches cause sub-daily timescale water-level oscillations that can pump lake water into and back-out of coastal areas such as rivermouths in a manner that is analogous to tides in estuaries.  Variations in seiche inputs are not as large as variations in tributary inputs across rivermouths, but nevertheless can result in dramatic differences in source-waters and mixing patterns among rivermouth systems.  These variations are in part due to differences in the seiche regime of the adjacent Great Lake (due to position of oscillation nodes, characteristic resonance times, etc. - Mortimer 2004, Trebitz 2006), and in part due to the local setting, addressed below.  

Depending on the volume of lake water inputs relative to tributary water inputs and prevailing circulation patterns, the location where lake water mixes with river water can be offshore of the system mouth (mixing in the plume only, depositional area is essentially river water) or within the depositional area (lake water intrusion, depositional area shows a gradient from river to lake water; Morrice et al. 2009, Morrice et al. 2011).  Water levels of the Great Lakes have predictable seasonal cycles (summer highs and winter lows), which together with seasonal cycles in tributary flows result in marked intra-annual variations in the degree of lake-water inputs to coastal systems (Morrice et al. 2004, DeCatanzaro and Chow Fraser 2011).  Differences among locations within and among lakes in the major current patterns, depth profiles, latitude, orientation and anthropogenic uses create variation in the character of Lake water inputs entering the rivermouth (Kerfoot et al. 2008) and in the magnitude and frequency of Great Lake inputs (Trebitz 2006).  Conversely, these factors also control where exports from the connecting water body are likely to be distributed, and the effects they have on other near-shore environments (Johengen et al. 2008). 

3.     Local setting

The local physiographic setting interacts with the river and lake hydrologic regime to determine local habitat conditions (e.g., bathymetry, sediment composition, shoreline exposure, etc.).  For example, surficial geology determine the degree to which receiving basins are carved by channels versus filled with sand or mud-flats, how steeply banks slope, and the ability of riverflows to restructure sediments.  The degree of exposure or shelter to wind and waves (fetch) is determined by local topography and shoreline orientation.  Water depth, fetch, substrate type, and bottom slope combine to determines the extent and zonation of aquatic vegetation (Geis 1985), thus the physiographic setting plays a substantial role in structuring a major habitat element of rivermouth ecosystems.  Local landform dictates the extent to which rivermouths develop floodplains, seasonally connected backwater areas, etc.   Local geomorphology influences the orientation of the opening from the rivermouth to the lake, with implications for mixing of plume water into a larger coastal zone.  The orientation and dimensions of the connection between rivermouth zone and the lake is important in dictating the exchange of biota and water, and can be influenced by local setting as well as by river size.  In some cases, sand or bedrock deposits at the rivermouth maintain an elevation difference between the lower rivermouth zone and the actual Great Lake, essentially preventing lakewater inflow and restricting access to fish and invertebrates that are not strong swimmers. Constrictions of the mouth also serve to attenuate seiche flow, even if no elevation gradient is present (Trebitz et al. 2002, Trebitz et al. 2009b).  Finally, basin area itself depends substantially on the local physiographic setting, and has implications forbiotic and abiotic processes[AST7] . Larger river mouth basins take in more total volume of lake water for a given seiche amplitude (Trebitz et al. 2005) - thus it is large river mouth systems, such as the St. Louis River entering western Lake Superior, where lake-water intrusions can be evident well upstream of the system mouth (Hoffman et al. 2010).[ADS8] 

4.     Human[G.L.C.9]  Alterations

At the downstream end of these altered landscapes are the rivermouths, where land use changes have been shown to impact the water chemistry and species composition of coastal wetlands (Brazner et al. 2007, Trebitz et al. 2009a), Great Lakes embayments (Yurista et al. 2009), and marine estuaries (Wigand et al. 2003).  Humans alter local rivermouth zone characteristics through actions related to infrastructure development in and adjacent to rivermouth zones (e.g., pier construction, dredging, building roadways and bridges, shoreline armoring). They also alter conditions locally via discharges of runoff and wastewater from various municipal uses including industrial cooling, stormwater or combined sewer/stormwater overflow, treated effluent, etc.  These anthropogenic influences tend to act synergistically to degrade rivermouth conditions.  For example, Kaur et al. (2006) have found that the combined effects of physical alterations by dredging and input runoff containing oxygen-demanding chemicals have created areas of low dissolved oxygen at some heavily industrialized rivermouths. Changes to nearshore bathymetry, substrate character, and energy regime resulting from physical shoreline modification tend to eliminate or drastically reduce emergent and submerged vegetation (Jude et al. 2005). Shoreline development has also been shown to be tightly correlated with invasions by plants with poor habitat value (e.g., Silliman and Bertness 2004).  In coastal areas with intense near-shore development, biotic communities may be disconnected from upstream watershed effects (Trebitz et al 2009a). Manipulation of estuarine floodplains for either flood protection (e.g., Smits and Nienhuis 2006) or water retention (e.g., Becker and Laurenson 2008) often leads to dramatic changes in biotic communities, sedimentation patterns and other structural properties. 

C.    Chemical Processes

            Quick ideas*[JHL10]* :

1.     Chemical Aspects of nutrients/contaminants loading from river/watershed and Great Lake.

2.     Different Micro-habitat processing environments: 

Lots of different habitat types means a mosaic of anaerobic and aerobic environments, different nutrient retention times, organic matter deposition and, as a result, different biogeochemical processing environments.

3.     Chemical gradients: 

In marine systems there are steep gradients in salinity, which are certainly less steep in Great Lakes (although potentially important).  However, thermal gradients may still create water "wedges" similar to those seen in marine systems with similar consequences.

D.   Biological Processes

Great Lakes rivermouths are presumed to provide unique local structure and function, as well as influence the ecological dynamics of entire Great Lakesecosystems.  Rivermouths serve as transition zones (ecotones) between fluvial upstream systems and offshore Laurentian Great Lakes environments, and also include unique habitats, such as rivermouth wetlands.  Thus, similar to other ecotones (e.g., estuaries, inland lake - river interfaces; Thiel et al. 1995, Willis and Magnuson 2000) the high degree of habitat variability present in Great Lakes rivermouths should facilitate a very diverse biotic ecosystem (cf. Bhagat and Ruetz in press).  In fact, various surveys of rivermouth wetlands have revealed a high degree of biotic diversity (Jude and Pappas 1992, Uzarski et al. 2005).

In addition to sustaining a high degree of biotic diversity, Great Lakes rivermouths are likely areas for 1) high rates of primary and secondary productivity (Wetzel 1992), and 2) important growth and nursery habitats for various key Great Lakes fish species.  Hydrologic properties of rivermouths will influence the diversity and productivity of these systems; in situations where the hydrodynamics are complex and a variety of retention areas are maintained, different wetland systems can form supporting a diversity of macrophytes and associated fauna.  In situations where the flow regime is highly channelized with limited retention, there will be less opportunity for different habitats to develop.  The system's nutrient loading regime discussed above has important influence on the biological conditions of the system.  For example, too much nutrient loading can result in near monocultures of nuisance and invasive macrophytes (Lougheed et al. 2001) and high densities of phytoplankton, including several toxin-producing strains of cyanobacteria (Hong et al. 2006, Xie et al. in press).  Nonetheless, high densities of phytoplankton should support large production of both pelagic and benthic invertebrates.

 Invertebrates in rivermouths will likely include both riverine and lacustrine forms, and in degraded rivermouths, sensitive invertebrates will likely be replaced by more tolerant taxa (Carter et al. 2006).  Höök et al. (2007) demonstrated that average zooplankton densities in Muskegon Lake are higher than in Lake Michigan, although Muskegon Lake zooplankton were dominated by small bodied forms.  There is strong evidence that rivermouths and plumes in a diversity of aquatic systems, including the Great Lakes, provide physical, chemical and biological environments that support high prey densities: these high prey densities in turn provide an ideal environment for young fish.

The role of rivermouths as important nurseries for fish stocks is particularly noteworthy for the overall Great Lakes ecosystem (Chubb and Liston 1986, Stephenson 1990, Hoffman et al. 2010, MORE).  Höök et al. (2007) found that young alewives in a drowned rivermouth lake (Muskegon Lake) emerged earlier, grew faster and potentially survived better than young alewives in Lake Michigan.  Even so, a competitive advantage for these rivermouth spawned fish does not necessarily imply these alewives make up a large proportion of the Lake Michigan population (Dufour et al. 2005), although in certain years this may be the case (Höök et al. 2008).  Additionally, drowned rivermouth lakes such as Muskegon Lake can serve as nursery habitats for juvenile lake sturgeon (for months and possibly years) as they move from their river of hatching to Lake Michigan (Altenritter 2010).

Ludsin (2000) found a significant positive relationship between spring discharge of the Maumee River and subsequent recruitment of yellow perch in Lake Erie.  A follow-up study by Reichert et al. (2010) did not find significantly greater densities of small perch in the Maumee plume waters, relative to non-plume waters. However, microchemical analysis of otoliths revealed that the Maumee plume provided a survival advantage for young perch, suggesting this advantage was created by a low light predation refuge.
We are not aware of other similar studies on other species in other rivermouth ecosystems.  However, many Great Lakes fishes are plastic spawners, using both tributary and lacustrine habitats.  Young fish undoubtedly make use of rivermouth, plume and non-plume lacustrine environments throughout the Great Lakes.  The relative importance of these different habitats to the overall health of the rivermouth system is likely to vary among lakes: the habitats of a rivermouth emptying into deep and productive waters might be much less vulnerable to alteration or degradation than a plume emptying into shallow, oligotrophic waters. [V.P.11] 

E.    Science and Research Needs

Many of the unresolved rivermouth research questions are overarching in nature, addressing physical, chemical, and biological issues. We first examine research needs within each discipline before identifying the more holistic information needs.

There has been a considerable amount of Great Lakes research and modeling focused on understanding the processes that lead to the export of sediments, nutrients, and other pollutants from watersheds.  The USACE Great Lakes tributary sediment reduction program is a good example of those efforts. However, relatively little has been done in the rivermouth transition between the watershed and the nearshore zone. 

Many programs exist to protect and restore, directly and indirectly, aquatic ecosystems (see Section IV B and C) and therefore can help also help rivermouth systems.  However, these programs fall short of addressing rivermouths as a distinct set of unique ecological systems.  What is needed to advance rivermouth science and management is a coordinated rivermouth program that includes integrated research, monitoring, and modeling at several sites that represent the different types of rivermouth ecosystems that are found across the Great Lakes.  The value of such a program is in the synergies gained from conducting simultaneous monitoring, research, and modeling.  Models supported by good data provide insight on ecosystem structure and functioning as well as the ability to make projections of how the system will respond to perturbations.  Research provides process understanding and parameterization for models.  And monitoring provides input and credibility for models.  This type of integrated program will allow scientists to develop a quantitative understanding of how various types of Great Lakes rivermouth areas function, which in turn can be used to help inform programs designed to preserve and restore these critical systems.

1.     Physical: 

As described above, rivermouth physical processes have been greatly altered through activities such as shoreline armoring, pier construction, harbor channel dredging, and road and bridge construction.  Yet, we still have only a rudimentary understanding of:

• 1) rivermouth water budgets (sources, fluxes, exports) and how they influence three-dimensional mixing processes in the various parts of rivermouths (Figure 3);
• 2) the relationship between the sources of water (Great Lake vs. land-delivered) and nutrients, sediment, and seston (suspended particles), despite the importance of this relationship to water quality and food webs of rivermouths and the Great Lakes (e.g., Peterson et al. 2007);
• 3) the effects of dredging and armoring on hydrogeomorphic processes and, therefore, nutrient processing due to reduced residence time;
• 4) the influence of physical disturbances (dredging, shoreline hardening, urban infrastructure and waterfront redevelopment initiatives) on wetlands and depositional areas that have become disconnected from riverine and lake influences, especially in highly developed harbors; and
• 5) the effects of roadway and culvert construction on these transitional ecosystems (Trebitz et al. 2005), similar to tidal channel blockage in saltwater estuaries caused by road construction (e.g., Turner and Lewis 1996). 

2.      Chemical:

Our lack of understanding of the chemical processes occurring in rivermouths severely limits our ability to predict nutrient exports to the Great Lakes.  The flow and nutrient monitoring framework for river systems in the Great Lakes basin is tremendous, but except for a few studies (e.g., Steinman et al. 2009) we do not know how the nutrients and flows are transformed within rivermouths and how they influence deepwater habitats and water quality in the Great Lakes proper.  Furthermore, to manage rivermouths on a landscape scale that includes watershed management, we need greater understanding of the effects of watershed properties on the nutrient loads to rivermouths (Allan et al. 1997). The effects of legacy and emerging contaminants on aquatic organisms inhabiting rivermouths, including the fish that we eat, is gaining interest, but greater understanding still is required, especially in these rivermouth zones, which is where the majority of AOCs are located in the Great Lakes (Madenjian et al. 2009).

3.      Biological:

There are at least three main categories of research needs for biological processes:  habitat quality and use, food webs, and aquatic-terrestrial linkages. 

a)      Habitat quality and use:  

Rivermouth habitats are important fish nursery and passage to upstream spawning grounds for adfluvial fishes such as white suckers, steelhead, and lake sturgeon among others (e.g, Zorn and Sendek 2001, Flecker et al. 2010). In fact, 61 of 114 Great Lakes fish species are migratory, according to life history accounts (e.g. Scott and Crossman 1973, Trautman 1981, Becker 1983, Zorn and Sendek 2001), yet we know very little about how, when, why, and to what extent these areas are utilized for this purpose.  Identifying the areas critical to nursery fish production, their habitat quality (Rutherford 2008), and sources of nutrients are critical for prioritizing restoration efforts.  Otolith, fatty acid, and stable isotope chemical signatures offer potential for addressing such questions (e.g., Brazner et al. 2004, Hoffman et al. 2010).  Furthermore, habitat quality has been dregraded in many areas due to shoreline alteration and invasive plant species, such as Phragmites.  The linkage between shoreline development and invasive plant establishment is well known (e.g., Silliman and Bertness 2004), but the extent to which this influences rivermouth habitat quality is not documented.

b)      Food webs:  

Determining estuary-dependent fish and wildlife species in the upper trophic levels of rivermouths food webs would help to link management efforts in deepwater areas with the nearshore.  Which species of greatest importance to rivermouths are also of importance to the Great Lakes fishery? Likewise, we need a better understanding of the nutrient exports and energy subsidies that rivermouth ecosystems provide to Great Lakes food webs (cf. Ogdahl et al. 2010). Tied to this is our emerging understanding of invasive species effects on nutrient cycling and foodwebs.  For example, dreissenids are altering both shallow water trophic interactions by increasing water transparency and stimulating increased benthic algal growth (Hecky et al. 2004) and deep water trophic structure by removing nutrients from the water column (Kerfoot et al. 2010, Mida et al. 2010, Nalepa et al. 2010, Vanderploeg et al. 2010), which begs whether dreissenids may be altering the effects of rivermouth exports on deepwater habitats in unforeseen ways.

 The role of wetlands as possible refuges for native species (Cooper et al. 2007) points to the importance of either maintaining or restoring the ecological integrity of these fragile ecosystems.  Invasive aquatic organism introductions may be more prevalent in rivermouth areas as well because of proximity to shipping channels.  The need to characterize their current status before further invasive-induced changes occur is paramount. 

Because rivermouths represent the transition zones between landscape and lake, understanding the quality and quantity of food sources and effects of watershed characteristics on those food sources is a further research need (e.g., Peterson 2007). 

Determining whether the lake or river provides the primary food sources for the various trophic levels within rivermouths, and whether they change over time, will help us understand the biological structure of these productive ecosystems and their energy contribution to deepwater areas.

c)      Aquatic-terrestrial linkages:  

Rivermouths also can serve as study areas for improving our understanding of linkages between aquatic and terrestrial systems. These subsidies can take many forms.  For example, carbon transport from the landscape clearly influences Great Lake dynamics (Biddanda and Cotner 2002), and is incorporated into the isotope chemistry of rivermouth fishes (Hoffman et al. 2010).  Less known is whether transient inputs from the Great Lakes into rivermouths also provide important chemical subsidies, although there are regions of the Great Lakes where lakewater has higher nutrient concentrations than water coming from the watershed (e.g., nitrogen in Lake Superior - Morrice et al. 2009, and in Lake Huron - DeCatanzaro and Chow Fraser 2011).   It is likely that, as in river systems (Polis et al. 1997, Nakano and Murakami 2001), a subsidy is provided to terrestrial fauna by rivermouth fish and insects; migratory birds also may bring nutrient subsidies from the Great Lakes to the arctic, as occurs from other ecosystems (Jeffries et al. 2004), necessitating a hierarchical understanding of how rivermouth ecosystems function within the greater landscape.  

IV.          Rivermouth Conservation and Management 

Describe the Management Framework for Rivermouth Ecosystems (based on our conceptual model)

 Conservation[1] of Great Lakes rivemouths falls within the purview of dozens of federal, state, and local agencies and organizations. At the same time, no single agency, organization or program is focused on rivermouth ecosystems as a unique target for conservation efforts.  Rather, rivermouth conservation occurs because it is part of another program that overlaps ecologically with rivermouth systems, such as wetland restoration programs, coastal zone management programs, nonpoint source control programs, Great Lakes Areas of Concern etc.  Below is a brief overview of the programs that address some part of rivermouth ecosystems.  They are broken down into the large-scale management efforts and local management efforts, paralleling the discussion of drivers in Section II above.

A.   Roles and Responsibilities

Regulatory authority over rivermouths in the United States stems primarily from the Clean Water Act (CWA; 1977) and the River and Harbors Act (RHA; 1899).  These acts insure that activities occurring within these areas require a permit and are thus subject to the National Environmental Policy Act (NEPA; 1970), thus requiring an environmental review (i.e., an environmental assessment or an environmental impact statement).  Permitting through this process also provides a legal nexus through which state and federal endangered species laws (e.g., U.S. Endangered Species Act [ESA] of 1973) assert jurisdiction:  As a federal action, the issuance of permits related to the CWA and RHA must not jeopardize endangered species.  In addition, the CWA resulted in the National Pollutant Discharge Elimination System (NPDES) Program, which essentially requires permitting for the release of all anthropogenic pollutants from point sources (again, subject to NEPA and ESA requirements).

These programs have narrow foci (e.g., endangered species or particular habitat types), and activities that may be considered harmful to the environment may not be subject to their jurisdiction.  Further, the effectiveness of programs associated with these acts varies (NRC 2001, Schwartz 2008).  For example, the destruction of wetlands is ostensibly forbidden by regulations and guidelines related to section 404 of the CWA, yet independent analyses have consistently shown that wetland destruction continues (NRC 2001). State agencies often enforce these national programs (e.g., NPDES) and may also have similar state laws that grant greater authority or result in different expectations.  These regulatory authorities do not constitute a management program, but do allow for a robust accounting of development activities occurring throughout the U.S. side of the Great Lakes.  To our knowledge, no specific programs in Canada address rivermouth ecosystems.  Canadian protection for wetlands, presumably including coastal wetlands and thus encompassing many rivermouths, is largely decentralized, with much of the authority retained in provincial governments (Rubec and Hanson 2009). 

To our knowledge, on the national level, management plans focused on estuarine systems as a class do not exist.  However, several organizations monitor and create management plans for Great Lakes coastal areas (including wetlands and estuarine systems).  Within the U.S., the Coastal Zone Management Act (CZMA; 1972) is administered by the National Oceanic and Atmospheric Administration, and provides for management of the nation's coastal resources, including the Great Lakes (http://coastalmanagement.noaa.gov/welcome.html). 

Every state with Great Lakes coastline has a coastal program[2] created under the CZMA authority that coordinates efforts to enhance and protect coastal areas.  Most rivermouth zones (a.k.a. estuaries) are included as "coastal" zones, and are a part of the management mandate of this program.  However, we are unaware of management actions or programs specifically focused on rivermouth systems as a group.[G.L.C.12] 

Several individual rivermouths have been the focus of targeted management efforts.  The National Estuarine Research Reserve System (NERRS), generated by the CZMA, focuses on rivermouth (estuarine) ecosystems.  Two Great Lakes estuaries are included in this reserve (Old Woman Creek in Ohio and the St. Louis River estuary in Wisconsin).  The St. Louis River estuary is also the focus of additional efforts by state and federal governments, as well as non-governmental organizations, coordinated by the Fish and Wildlife Services' Coastal Program (Patrick Collins, pers. comm.). 

B.    Watershed Scale Conservation Programs

1.      Watershed management

2.      Nonpoint source control

3.      Coastal management_____

4.      Climate Change ___

5.      Other??__

C.   Local Conservation and Management Programs and Activities

1.      Land Use management

2.      Wetland conservation

3.      NPDES/point source control

4.      Habitat and Special Area management (parks, beaches, etc)

5.      Ongoing Human/Societal Uses  (specific programs to mitigate their impacts)

6.      Other?)

The management of Great Lakes rivermouths is complicated by the multiple influences they experience (Figure 1).  While it may be possible manage contaminants from the watershed through regulatory or incentive-based processes (e.g., TMDLs), rivermouths also are influenced by both the receiving basin itself (which varies in time and space) and the offshore Great Lake (Figure 1).  Hence, regardless of whether the conservation or management focus is preservation (or relatively undisturbed rivermouths) or restoration (of disturbed rivermouths), activities must occur at multiple scales and be well-coordinated.

D.   Management Needs

Specific things to be done (to be developed after Sections IV-A-C are drafted)

1.     Monitoring and Evaluation

2.      Implementation

3.     Prioritizing protection and restoration/decision support tools -

4.     Promote a Systems approach

5.      Link science and restoration to economic growth, sustainability and quality of life

6.     Public Policy to support rivermouth conservation

7.     Advocacy/Education and outreach

V.  Creating A Rivermouth Collaboratory- "How to Make it Happen" 

(3 pages max plus graphics)

A.    Coordinating and Implementing Rivermouth Science, Management, and Policy

B.     Sustaining the collaboratory

C.    Coordinative Science Forums  

e.g. social media, other information-sharing mechanisms etc.

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[1]Conservation is defined as "the protection, preservation, management, or restoration of natural environments and the ecological communities that inhabit them. Conservation is generally held to include the management of human use of natural resources for current public benefit and sustainable social and economic utilization. conservation. (n.d.). The American Heritage® Science Dictionary. Retrieved December 20, 2010, from Dictionary.com website: http://dictionary.reference.com/browse/conservation
[2]Illinois Coastal Program is expected to be final in 2011.

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 [G.L.C.1]Is this heading intuitive?
 [G.L.C.2]Add reference to GLC recreational boating report - VP.
 [G.L.C.3]Is this header intuitive?
 [G.L.C.4]Reference needed.
 [G.L.C.5]Reference needed.
 [G.L.C.6]Relocated from Section IIIE because it describes the process which is the subject of this section  more than a research or science need which is the subject of section III-E..
 [AST7]Should be possible to say something about area affecting biota too - but I didn't have anything handy.  (is spawning area limited?  benthic productino?).
 [ADS8]Have to be careful here---is it really basin area or the rivermouth shape and gradient that is key here?  A small but very open system may be influenced to a far greater degree (in terms of percent of system affected) than a large but very constricted system.  This is also true for estuaries. 
 [G.L.C.9]Proposed header as the section below is focused on human alterations (previously discussed in Section IIB)
 [JHL10]Didn't get to this.  Essentially, these three sections are completely interwoven, but I think these are the kinds of things we need to think about for this section.
 [V.P.11]Edits were made to this sentence  so that it would read more clearly.  Verify that intent is correct.
 [G.L.C.12]Add Coastal and Estuarine Land Conservation Program as an example of a program that covers a majority of the nearshore environment. This program funds protection via easement or acquisition.
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