Rivers & Lakes


F1 Rivers and streams, F2 Lakes, FM1 Semi-confined transitional waters, MFT1 Brackish tidal systems, MT3 Anthropogenic shorelines, MT1 Shoreline systems

Rivers and streams

biome is comprised these Ecosystem Functional Groups (EFG): Permanent upland streams, Permanent lowland rivers, Freeze-thaw rivers and streams, Seasonal upland streams, Seasonal lowland rivers, Episodic arid rivers, Large lowland rivers. Rivers and streams include lotic (running water) ecosystems, flowing from elevated uplands or underground springs to deltas, estuaries, and lakes. They are defined primarily by their linear structure, unidirectional flow regimes, and close interaction with the surrounding landscape. Individual rivers drain catchments separated by watersheds. Channels that make up a river system can be classified into stream orders, with 1st order streams having no tributaries, 2nd order streams having 1st order tributaries, 3rd order having 2nd order tributaries and so on. The world’s largest rivers are 10th-12th order. Flow regimes depend on stream order and rainfall patterns in the catchment (except in regulated rivers and spring-fed streams), which vary from year-round to seasonal to episodic. Stream gradients determine flow velocity and turbulence, bank and substrate structure, and habitat variability, but flow variability depends on regional climate and local weather. River systems in arid zones may remain dry for several years. These factors act as selection filters, differentiating lotic ecosystems and their species’ traits amongst flow regimes, and between uplands and lowlands. Productivity tends to increase from uplands to lowlands and is driven both by allochthonous energy sources that contribute coarse organic matter from terrestrial ecosystems in adjacent riparian zones and upper catchments, and by autochthonous energy synthesis by biofilms or phytoplankton. Phytoplankton is important downstream in larger, slower rivers that carry smaller organic particles and more dissolved organic matter. Erosion and depositional processes depend on the gradient and position of a stream reach within a catchment, and are fundamental to downstream passage of nutrients and organic matter and exchange between river ecosystems and surrounding land. Anthropogenic nutrient inputs increase downstream and vary with land use. Rivers with extensive peatlands in their catchments are rich in tannins, which reduce light penetration through the water column, increase acidity, promote microbial activity that thrives on dissolved organic carbon, and thereby reduce oxygen levels, productivity and biotic diversity, although endemism may be high. Streams in cold climates freeze over in winter, imposing seasonal constraints on productivity and the movement of organisms. Much of the biotic diversity resides in or on the stream benthos. Trophic webs are more complex in large rivers due to greater resource availability and niche diversity, and species-catchment area relationships. Invertebrate detritivores consume fragments of organic matter, providing resources for predatory macroinvertebrates and fish, which in turn support larger predatory fish, waterbirds, reptiles, and some mammals. Specialised species-level traits are associated with different flow regimes and life history strategies often align with patterns of resource availability. For example, suspension feeding is common in high flow velocities, cold tolerance and seasonal dormancy occur in freeze-thaw streams, life cycles are geared to autumnal leaf fall in temperate forested catchments, and desiccation tolerance and dormant life stages dominate in episodic rivers.


biome is comprised these Ecosystem Functional Groups (EFG): F2.1 Large permanent freshwater lakes, Small permanent freshwater lakes, Seasonal freshwater lakes, Freeze-thaw freshwater lakes, Ephemeral freshwater lakes, Permanent salt and soda lakes, Ephemeral salt lakes, Artesian springs and oases, Geothermal pools and wetlands, Subglacial lakes. The Lakes biome includes lentic ecosystems defined by their still waters. They vary in area, depth, water regime and connectivity to other aquatic systems across a global distribution. Gradients in water regimes, temperature, lake size and salinity (and salt composition) exert critical influences on the function, productivity, diversity and trophic structure of lake ecosystems. Water regimes vary from permanent open waters to seasonal or episodic filling and drying on interannual time scales. Lakes span global climatic gradients, which influence their water regimes through catchment precipitation and evapotranspiration rates, as well as the seasonal freeze-thaw cycles of lake surfaces along latitudinal and altitudinal temperature gradients. The azonal character of the Lakes biome, however, is due to the buffering of climatic influences by groundwater, geomorphology, and substrate. This is most evident in the water regimes of artesian springs, oases and geothermal wetlands, as their water sources are largely independent of climate. Lake and catchment substrates influence nutrient stocks and salinity, but concentrations may vary temporally depending on water regimes and mixing. Deeper and freeze-thaw lakes are often characterised by stratification, producing depth gradients in nutrient and oxygen availability and temperatures. The deepest lakes extend to the aphotic zone. Productivity is determined by allochthonous inputs from the catchments and autochthonous inputs from phytoplankton, periphyton (i.e. biofilms), and submerged, floating and emergent macrophytes. Trophic webs tend to increase in size and complexity with lake size due to increased resource availability and niche diversity, but small shallow lakes have greater diversity than small deep lakes due to habitat heterogeneity and light penetration to the bottm allowing development of benthic macrophytes and associated biota. Salt lakes may have high productivity but simple trophic structures, with high abundances of few species. Invertebrate detritivores consume fragments of organic matter, providing resources for macroinvertebrates, fish, waterbirds, reptiles and mammals. Species traits appear to be strongly influenced by environmental filtering by the water regime (e.g. cold tolerance and seasonal dormancy occurs in freeze-thaw lakes and desiccation tolerance and dormant life stages dominate in ephemeral lakes) and water chemistry (i.e. tolerance to salinity in salt lakes).

Semi-confined transitional waters

biome is comprised these Ecosystem Functional Groups (EFG): Deepwater coastal inlets, Permanently open riverine estuaries and bays, Intermittently closed and open lakes and lagoons. The Transitional waters biome includes coastal inlets that are influenced by inputs of both fresh and marine water from terrestrial catchments and ocean tides, waves and currents. They include deep-water coastal inlets or fjords mostly restricted to high latitudes, as well as estuaries, bays and lagoons, which are scattered around coastlines throughout the world. Gradients in water regimes, water chemistry, depth, temperature, size and salinity influence the function, productivity, diversity and trophic structure of these transitional ecosystems. The balance between marine or freshwater influences varies seasonally and inter-annually, depending on the climate and among inlets with differing geomorphology, catchment size, climate and exposure to waves and currents. In some cases, ecosystems characteristic of the marine shelf biome (i.e. M1.1 Seagrass meadows) may have significant occurrences within semi-confined transitional waters. Some inlets are permanently connected to the ocean, but others are only intermittently connected, influencing exchanges of water, nutrients and biota among ecosystems. The dynamics of connection and closure of shallow inlets are regulated by variations in steam flow inputs and wave activity. Strong horizontal and vertical salinity gradients (varying with freshwater and marine inputs) structure biotic communities and traits that equip species for occupying different salinity niches. Autochthonous energy generated by primary production from aquatic macrophytes, phytoplankton, macroalgae and diatoms is subsidised by allochthonous inputs from inlet shorelines, freshwater streams and marine incursion. These high levels of energy availability support complex trophic networks, including large populations of macroinvertebrates, fish, waterbirds, seabirds and some mammals and reptiles. Many inlets function as fish nurseries and bird breeding sites.

Brackish tidal systems

biome is comprised these Ecosystem Functional Groups (EFG): Coastal river deltas, Intertidal forests and shrublands, Coastal saltmarshes and reedbeds. The Brackish tidal systems biome is associated with prograding depositional shorelines at the interface of terrestrial, freshwater, and marine realms. The relative influences of marine, freshwater, and terrestrial processes vary from strongly fluvial deltas to marine-dominated intertidal forests and terrestrial-dominated coastal saltmarsh. Autochthonous sources of energy, contributed by flowering plants and algae, are supplemented by allochthonous sources delivered by rivers, currents, and tides. These sources support high productivity and complex trophic webs that include highly mobile fish and birds that rely on brackish tidal systems to complete their lifecycles. Standing plants assimilate energy and engineer habitat structure for epifauna and epiflora as well as juvenile fish nurseries. They also promote sediment deposition by dampening wave and tidal energy. While terrestrial systems are the ultimate source of most sediment, fluvial and marine processes redistribute it and drive patch dynamics across temporal and spatial scales. Brackish tidal systems are structured by steep local gradients in salinity and tidal exposure. Physiological traits that confer differential fitness and competitive abilities, together with differential predation pressure, mediate species turnover along gradients. Brackish tidal systems are distributed on depositional coastlines throughout the world.

Anthropogenic shorelines

biome is comprised of the Ecosystem Functional Groups (EFG): Artificial shores. The Anthropogenic shorelines biome is distributed globally where urbanised and industrial areas adjoin the coast, and includes some more remote structures such as artificial islands. It includes marine interfaces constructed from hard, smooth surfaces, including concrete, timber, lithic blocks and earthen fill, adjoining, extending or replacing natural shores, or floating in proximity to them. These relatively homogeneous substrates support an opportunistic, cosmopolitan biota with limited diversity and simplified trophic structure compared to other shoreline systems. Vertical surfaces are inhabited by algae and biofouling species but are exposed to strong tidal desiccation regimes that strongly filter potential colonists. Floating structures have downward-facing, usually smooth, surfaces, unlike almost anything in nature, which may be colonised by opportunists. Influx of storm water and effluent enhances nutrient levels and eutrophic algae, which contribute autochthonous energy. Outflows from developed areas are also major sources of allochthonous energy. Strong bottom-up regulation stems from these resource inputs and from low populations of predators, which are depleted or deterred by human activity.

Shoreline systems

biome is comprised these Ecosystem Functional Groups (EFG): Rocky shores, Muddy shores, Sandy shores, Boulder and cobble shores. The Shoreline systems biome comprises naturally formed, intertidal abiogenic habitats situated at the interface between land and sea. The distribution of the biome spans all latitudes (temperate to polar) at which landmasses are present. Productivity ranges from high to low, is loosely proportional to the availability of stable hard substrate for macrophyte attachment and inversely proportional to the dependency on allochthonous energy sources derived from both land and sea. Productivity is also influenced by coastal upwelling and, for ecotypes of finer particle size, the nutrient content of adjacent terrestrial sediments. Within and across ecotypes, biotic communities are strongly structured by tides, waves and particle size, ranging from contiguous rock to fine silts and clays. Notably, some shorelines comprise mixed hard and soft substrates, with vertical zonation varying temporally in response to storm events and redeposition of soft sediments. Tides produce a vertical gradient of increasing aerial exposure across which desiccation and temperature stress increase, time available for filter-feeding decreases, and interactions with marine and terrestrial predators vary. Waves and particle size determine substrate stability and the physical disturbance regime. Wave action, diminishing from headlands to bays, produces horizontal gradients in community structure. Many organisms possess morphological and behavioural adaptations to prevent desiccation at low tide and dislodgement by wave forces. Burrowing animals are important in unconsolidated sediments. Competition (especially for space) is a major factor structuring communities, with its importance diminishing with decreasing particle size. Facilitative interactions (particularly those that protect organisms from desiccation stress or physical disturbance) can be important across ecosystems of all particle sizes. Biodiversity is generally high, with microscopic lifeforms dominating the biomass of systems of small particle size.


Rivers and lakes biome is comprised of: rivers; Lakes, freshwater; Lakes, saltwater; Human made water bodies; Other (rivers and lakes)


FEMA uses two definitions under the title “Riparian”:

U.S. Fish and Wildlife Service

Areas where plant communities are contiguous to and affected by surface and subsurface hydrologic features of perennial or intermittent lotic and lentic water bodies (rivers, streams, lakes, or drainage ways). Riparian areas are usually transitional between wetland and upland. Riparian areas have one or both of the following characteristics: 1) distinctly different vegetative species than adjacent areas; 2) species similar to adjacent areas but exhibiting more vigorous or robust growth forms.

USDA’s Natural Resources Conservation Service

Riparian areas are ecotones that occur along watercourses or water bodies. They are distinctly different from the surrounding lands because of unique soil and vegetation characteristics that are strongly influenced by free or unbound water in the soil. Riparian ecotones occupy the transitional area between the terrestrial and aquatic ecosystems. Typical examples would include perennial and intermittent streambanks, floodplains, and lake shores.


ESRI, USGS, and Dynamic World use primarily Water for this category. Flooded vegetation can fit into the Riparian category.

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