Aquatic-terrestrial subsidies
[8] These inputs of resources can influence individual growth, species abundance and diversity, community structure, secondary productivity and food web dynamics.
[19] Stream invertebrates such as stoneflies, caddisflies and midges also derive energy and nutrients from salmon and, in turn, provide food to terrestrial species such as birds and bats.
[19] Lateral movement of nutrients and energy from the stream to the surrounding riparian zone and terrestrial environment beyond serve an important role in food webs.
[20] Algae and fine organic matter washed up from high flows provide resources to herbivorous species and promote plant germination.
[21] Emergence of aquatic insects typically peaks in the summer of temperate zones, prompting predators to aggregate and forage along riparian and stream boundaries.
[19] Brown bears have been shown to deliver as much as 84% of the nitrogen found in white spruce trees that are up to 500 meters from the stream on the Kenai Peninsula (Alaska, USA) through their interactions with aquatic subsidies.
[22] Aquatic subsidies, however, can be extremely important in the terrestrial landscape and are generally of higher nutritional quality because they come from animal, rather than plant-based or detrital, sources.
[10] Global warming and habitat modification change both the physiology and phenology of emerging aquatic insects as well as the physical boundary between water and land, which in turn affects their dispersal.
[26] Terrestrial subsidies are primary production on land that is transferred to aquatic ecosystems as litter fall or dissolved organic matter.
[33] Terrestrial leaf litter, wood inputs and deposition of pollen are important organic matter sources that augment benthic invertebrate productivity.
[8] Benthic invertebrate communities respond swiftly to changes in the supply of organic matter; the absence of litter stocks led to a drastic decline in productivity and predators in one experimental temperate stream system.
[8] Furthermore, provision of organic matter may increase productivity and create hypoxic conditions in streams; however, this is typically uncommon given the high turnover and low residence time of water.
[34] In the Mara River basin, though, substantial rates of organic matter and nutrient loading by hippopotami create subsidy overloads in hippo pools, stimulate anoxic conditions approximately three times a year, and cause multiple fish kill events.
[34] Aquatic-terrestrial contaminant subsidies originating in the aquatic environment can be transported across ecosystem boundaries, primarily mediated by organisms.
[40] Various organic compounds, trace elements, metals, algal toxins, pesticides, and pharmaceutical waste products resulting from intentional or incidental releases via human activities can act as contaminant subsidies.
[37][41][42][43][44][45] After being loaded into waterways, contaminants that accumulate in the aquatic food web can return to terrestrial environments through consumption by organisms.
[48] One, that contaminants like metals and polycyclic aromatic hydrocarbons (PAHs) are preferentially shed into the exoskeleton during metamorphosis, and then recycled into the aquatic environment.
[49][50] Three, larval aquatic macroinvertebrates can transfer contaminant subsidies directly to terrestrial environments following successful metamorphosis to their adult form.
[50] Subsequent consumption of fish from aquatic environments by terrestrial predators is a significant movement pathway for aquatic-terrestrial subsidies.
Consumption of animals containing these contaminants by terrestrial predators is another pathway of aquatic-terrestrial subsidy transfer across large spatial scales.
[49] Consuming these contaminated prey items can result in severe histological, circulatory, digestive, and reproductive issues in terrestrial predators like spiders, amphibians, reptiles, mammals, and birds.
[46][58][59] The large number of insects that some predators need to consume in proportion to body mass for survival raises the risk of contaminant bioaccumulation, increasing the likelihood of developmental deformities and mortalities.
[49][44][64] The subsequent reduction in recruitment from a lack of prey or consumption of contaminant subsidies can lead to local extirpations of fish, and aquatic and arachnivorous birds.
[69][70] Naturally-occurring variation in carbon stable isotope ratios can often distinguish organic matter produced by photosynthesis of terrestrial plants or aquatic algae.
[30] There is sometimes overlap between terrestrial plants and algae in naturally-occurring stable carbon isotope ratios, complicating their use in identifying aquatic-terrestrial subsidies.
[71] Stable isotope ratios of nitrogen are particularly useful in tracing fluxes of marine-derived resources such as anadromous fish into riparian and terrestrial environments.
Aquatic insects are commonly studied to estimate water quality because many species are highly sensitive to pollution, resulting in community composition changes in contaminated waterbodies.
