Landscape Limnology Primer

Landscape limnology = the spatially-explicit study of lakes, streams, and wetlands as they interact with freshwater, terrestrial, and human landscapes to determine the effects of pattern on ecosystem processes across temporal and spatial scales (Soranno et al. 2010).

The phrase ‘Landscape Limnology’ was first coined by Dr. Wayne Wurtsbaugh from Utah State. This subdiscipline was then developed by Drs. Patricia Soranno, Kendra Spence Cheruvelil, Mary Tate Bremigan, and Katherine Webster during the early 2000’s. These researchers championed the perspective that lakes, streams, and wetlands, as well as freshwater and terrestrial landscapes, are integrally connected ecosystems and landscapes, and thus should be studied and managed that way.

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Patricia A. Soranno, Kendra S. Cheruvelil, Katherine E. Webster, Mary Tate Bremigan (L-R). Circa 2007

Principles of landscape limnology (adapted from Soranno et al. 2010)

Four core principles or themes of landscape ecology (synthesized by Wiens 2002), adapted for lakes by Soranno et al. (2009), and expanded more broadly to all freshwater ecosystems by Soranno et al. (2010) to provide the foundation for landscape limnology.  Figures below are drawn from the perspective of a lake. A patch = a lake.

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Patch Characteristics

Individual lake, stream and wetland ecosystems can be considered patches characterizedImage: Patch Characteristics. Figure is drawn from the perspective of a lake. A patch = a lake. by physical, chemical, and biological features such as water chemistry, species richness, and primary and secondary productivity. These patches have boundaries, which are often more easily defined for freshwater ecosystems than for terrestrial ecosystems (e.g., shoreline, riparian zones, and emergent vegetation zone) and are often a focal-point for important ecosystem processes linking freshwater, terrestrial, and human landscapes.

 

 

 

Patch Context

An individual ecosystem is embedded in a complex mosaic defined by the freshwater, Image: Patch Context. Figure is drawn from the perspective of a lake. A patch = a lake.terrestrial, and human landscapes. The explicit spatial location of these patches and their placement relative to other landscape elements, both past and present, determines the attributes and dynamics of each ecosystem and its functional processes.

Land use/cover is a well-studied driver of freshwater ecosystems that integrates elements of freshwater, terrestrial, and human landscapes. For example, lake nutrients are influenced by adjacent wetlands and forests and altered by human activities in the catchment such as agriculture and urbanization. In this example, the land use/cover immediate surrounding Lake A is undisturbed forest with nearby wetlands while Lake B is immediately surrounded by wetlands, with agricultural and suburban land use/cover prevalent nearby.

 

Patch Connectivity & Directionality

Individual ecosystems are connected within the freshwater landscape by hydrologic Image: Patch Connectivity. Figure is drawn from the perspective of a lake. A patch = a lake.flowpaths through both surface water and groundwater. These flowpaths define the movement of materials, such as dissolved ions, nutrients and sediments, and organisms among ecosystems and display a strong directionality in connectivity that must be explicitly considered (e.g., Kling et al. 2000). The location of an ecosystem along the hydrologic flowpath defined by the freshwater landscape explains spatial heterogeneity in a range of physical, biological and chemical properties. For streams, the River Continuum Concept (RCC) of Vannote et al. (1980) was the first to conceptualize a longitudinal pattern in attributes and processes from headwaters to lowland reaches. For lakes and wetlands, Kratz et al. (1997) and Winter et al. (1991) developed frameworks conceptualizing analogous longitudinal patterns. In this example, in general, a headwater lake (A) would have a smaller surface area, lower conductivity, and fewer fish species than a lowland lake (B).

 

 

Spatial Scale & Hierarchy

Individual patches are influenced by interactions among freshwater, terrestrial, and Image: Spatial Scale & Hierarchy.human landscapes that occur at multiple spatial and temporal scales and that are hierarchically structured. Understanding these spatial hierarchies is a critical aspect of landscape limnology because (a) the characteristics of individual freshwater ecosystems are constrained by processes at higher spatial scales (Frissell et al. 1986, Tonn 1990, Poff 1997); (b) the degree of homogeneity among freshwater ecosystems can change in relation to the scale of observation; and (c) management and policy influencing a freshwater ecosystem are set at multiple spatial scales, from local to national levels.

For example, at the broadest spatial scale, biomes are shaped by climate, geology and landform, which act as constraints on the range of potential characteristics of observed within them. At the ecoregion scale, additional constraints related to finer scale spatial heterogeneity in features such as geology, soils, and landform are imposed, further limiting limnological expression. Lake characteristics are further defined by position within a hydrologic flowpath, which determines the strength and pattern of freshwater connections. Finally, individual lake characteristics (such as morphometry or the spatial arrangement of within lake habitat types) act within all the above constraints.

Conceptual Framework

 The four principles described previously are integrated into the landscape limnology Image: Landscape Limnology Conceptual Framework.conceptual framework (see above, and Soranno et al. 2009, and 2010). The ‘funnels’ represent freshwater, terrestrial, and human landscapes. These three funnels each possess unique properties and functionality, but collectively comprise a complete landscape mosaic that influences freshwater patches. Ovals depicted in the funnels of the landscape limnology framework are organized hierarchically and provide examples of landscape-context variables known to be important drivers of freshwater ecosystem variation. All ultimately contribute towards explaining among-ecosystem heterogeneity in a response variable of interest. The framework is flexible in that, depending on higher-level constraints, different sets of specific landscape-context variables can be included – for example, lakes in a high-elevation alpine setting will be controlled by different factors from lakes in a flat non-glaciated setting. Further, one can explain variation at other focal spatial scales either above or below the focal scale of a lake, stream or wetland that we use here.