User:Cedwards96/Aquatic-terrestrial subsidies

Note: all content is new (ie not revised) aside from two sections that were copied from the original, indicated below. We focused on adding the ecotox components to the article rather than editing existing portions as another college class will be doing that.

Copied from original article: ((Energy, nutrients, and contaminants derived from aquatic ecosystems and transferred to terrestrial ecosystems are termed aquatic-terrestrial subsidies or, more simply, aquatic subsidies. The most common examples of aquatic subsidies involve organisms that move across habitat boundaries and deposit their nutrients as they decompose in terrestrial habitats or are consumed by terrestrial predators, such as spiders, lizards, birds, and bats. This phenomenon is exemplified by aquatic insects that develop within streams and lakes before emerging as winged adults and moving to terrestrial habitats. Fish removed from aquatic ecosystems by terrestrial predators are another important example. Conversely, the flow of energy and nutrients from terrestrial ecosystems to aquatic ecosystems are considered terrestrial subsidies; both aquatic subsidies and terrestrial subsidies are types of cross-boundary subsidies.))

Contaminants as aquatic-terrestrial subsidies (Chloe)
Aquatic-terrestrial contaminant subsidies originating in the aquatic environment can be transported across ecosystem boundaries, primarily mediated by organisms. The transmission of contaminants can have negative ecological consequences that amplify up the food chain, including reduced nesting success of birds, disruptions to riparian food webs , and contamination of otherwise pristine environments. The mechanism of aquatic-terrestrial contaminant transfer of can be especially influential when there are no additional  sources of those contaminants to the terrestrial system.

Types of contaminant subsidies (Annika)
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. After being loaded into waterways, contaminants that accumulate in the aquatic food web can return to terrestrial environments through consumption by organisms.

Movement pathways through animals (Chloe)
Organisms serve as the vector for transportation of contaminant subsidies across trophic levels and aquatic-terrestrial ecosystem boundaries. Understanding the fate of aquatic-terrestrial subsidies is key to predicting their impact on terrestrial consumers.

Invertebrates (Chloe)
Aquatic invertebrates take up contaminants introduced to the environment via the water column, by grazing on surfaces, and from contaminated sediment. These contaminants can have several fates depending on their biochemical properties. 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. Two, macroinvertebrates eaten during aquatic or larval stages transfer their contaminant burdens to higher aquatic trophic levels such as fish and those contaminants are retained by the aquatic environment. Contaminants that would otherwise be shed during metamorphosis are therefore most likely to be taken up by aquatic predators of larval stage insects. Three, larval aquatic macroinvertebrates can transfer contaminant subsidies directly to terrestrial environments following successful metamorphosis to their adult form. In particular, man-made organic contaminants like polychlorinated biphenyls (PCBs) can become concentrated in adults. Predator risk for the uptake of organic contaminants is higher when preying upon adult life stages of aquatic insects, and adult aquatic insects are more likely to be consumed by terrestrial predators such as birds. Terrestrial predatory invertebrates have also been identified as vectors of contaminant transport. In particular, riparian spiders have been shown to move contaminants, such as methylmercury, originating in aquatic prey to the terrestrial environment.

Fish (Chloe)
Because many fish species prey upon macroinvertebrates that may have taken up contaminants, fish are an important middle trophic level for contaminant transport. Subsequent consumption of fish from aquatic environments by terrestrial predators is a significant movement pathway for aquatic-terrestrial subsidies.

Anadromous migratory fish, such as salmon, transport contaminants far distances and across aquatic ecosystem boundaries. The consumption of salmon by terrestrial predators, such as bears, when salmon return to freshwater ecosystems to spawn transfers marine-derived contaminant subsidies to terrestrial systems far removed from areas of contaminant uptake by the aquatic food web. Salmon can be the largest dietary source of marine-derived contaminants consumed by bears. Salmon-derived contaminants are also transported to recipient aquatic ecosystems where salmon spawn and/or die. Contaminants may be maternally transferred to eggs or recycled to the base of aquatic food for subsequent trophic transfer to higher trophic levels. Consumption of animals containing these contaminants by terrestrial predators is another pathway of aquatic-terrestrial subsidy transfer across large spatial scales.

Birds (Chloe)
Fish-eating birds are at the topmost trophic level of many aquatic food webs. As a result, birds are often the recipients of aquatic contaminant subsidies and transporters of aquatic contaminants to the terrestrial environment. An area of much research in birds is the tendency for contaminants present in the aquatic environment to biomagnify to significant levels in predatory birds. This phenomenon was exemplified by DDT biomagnification in predatory birds during the 1960's in the US, which resulted in the collapse of many bird populations.

Migratory birds share the same capacity for contaminant transport across vast distances as fish. This may be of particular concern with Arctic migratory birds, as they have the ability to transport contaminants to environments with otherwise limited contaminant input. Birds can also recycle contaminants back to aquatic environments via guano.

Impacts of contaminant subsidies on terrestrial predators (Annika)
For flies and other metamorphosing insects, high burdens of Se, PCB, metals, synthetic nanoparticles, and other contaminants can decrease body and reproductive fitness, leading to reduced amounts of larvae metamorphosing and emerging from the water column as terrestrial adults. When contaminant exposure does not impact metamorphosis or emergence, emerging insects may carry high concentrations of contaminants that are readily bioavailable to the terrestrial food web. 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. 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. This also can result in the biomagnification of organic and element subsidies like PCBs, selenium, and mercury by higher trophic levels that consume contaminated aquatic insects and their primary consumers like arthropods and fish. Contaminant levels in prey can be so highly concentrated that, for example, small-bodied songbird chicks can experience adverse physiological effects from feeding on a single spider containing high levels of PCB (at less than 6,000 parts per billion).

Ecosystem-wide impacts (Annika)
Concentrated contamination of aquatic insect populations can facilitate a decline in the ecological health of aquatic and terrestrial ecosystems. Consumption of contaminated insects either continues the contaminant pathway up trophic levels or excretion returns the subsidies back into the sediment, a major sink of contaminants in aquatic environments. Due to the movement of subsidies through lotic systems and emergence patterns of flying insects, the source of contamination can be some distance away from the source of contamination and affected habitats. Furthermore, the massive biomass of insects compared to other animals, and the sequestration of organic contaminants in one water body, can lead to large amounts of contaminants being exported across many different terrestrial ecosystems. From a single creek, it was estimated that emerging insects exported around 6 grams of PCBs per year to land, which is equivalent to the amount exported by 50,000 migrating salmon in an entire watershed. 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. The loss of biomass and reduced subsidy pathways deteriorate the complexity of aquatic and terrestrial food webs. As the biodiversity of a habitat decreases, its ecological resilience to further contamination and food web restructuring also declines.

Measuring aquatic-terrestrial connections
Copied from original article: ((Researchers use several tools to assess how terrestrial and aquatic food webs are connected. Stable isotopes, particularly of carbon, nitrogen, hydrogen, and oxygen, can be used to determine what resources consumers are eating. Other compounds, such as fatty acids, can also be used to trace food web connections between aquatic and terrestrial ecosystems. ))

Measuring contaminant subsidies and impacts (Annika)
The movement of aquatic-terrestrial contaminant subsidies can first be measured by testing the water quality of sites with known contamination or near urban centers or factories that discharge chemical waste. This enables scientists to determine where contaminants are highly concentrated in aquatic habitats. Next, aquatic insects are often collected and analyzed for contaminant loads and to model any population changes. 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. Finally, researchers study histological, blood, gut, feather, and egg samples from predators to determine if contaminants are traveling up trophic levels via the consumption of contaminated prey and what negative effects this may have on predators.