Salmon‐derived nutrient and organic matter fluxes from a coastal catchment in southeast Alaska

Abstract

Salmon are important vectors for biogeochemical transport across ecosystem boundaries. Here we quantified salmon contributions to annual catchment fluxes of nutrients (N and P) and organic matter (C, N, and P) from a forested catchment in coastal southeast Alaska. Concentrations of ammonium and soluble reactive phosphorus increased by several orders of magnitude during spawning and were significantly correlated with spawning salmon densities. Nitrate concentrations increased modestly during spawning and were not significantly correlated with salmon densities. Salmon had a modest legacy effect on inorganic N and P as evidenced by elevated streamwater concentrations past the end of the spawning period. Dissolved organic carbon concentrations did not respond to the presence of salmon; however, concentrations of dissolved organic nitrogen and phosphorus showed a significant positive relationship to salmon densities. Changes in spectroscopic properties of the bulk streamwater dissolved organic matter pool indicated that streamwater dissolved organic matter became less aromatic and biolabile during spawning. On an annual basis, salmon were the dominant source of streamwater fluxes of inorganic nutrients, accounting for 92%, 65%, and 74% of annual streamwater fluxes of ammonium, nitrate, and soluble reactive phosphorus, respectively. In contrast, fluxes of organic matter were dominated by catchment sources with salmon accounting for <1% of the annual catchment flux of dissolved organic carbon and 12% and 15% of the annual fluxes of dissolved organic nitrogen and phosphorous respectively. These findings indicate that, in small coastal catchments, salmon can be a quantitatively important source of dissolved streamwater nutrients with implications for productivity in downstream estuarine ecosystems.

Non‐native Chinook salmon add nutrient subsidies and functional novelty to Patagonian streams

“…For example, seabirds and anadromous fish bring marine‐derived nitrogen and phosphorus into terrestrial and freshwater ecosystems (e.g. Graham et al., 2018; Hood et al., 2019; Walsh et al., 2020), and the widespread collapse of seabird and anadromous fish populations has resulted in the global transfer of phosphorus from sea to land declining over 96% from historic levels (Doughty et al., 2016). Whereas the loss of historic connections among ecosystems disrupts nutrient cycles and recipient food web productivity (Gresh et al., 2000), the emergence of novel resource linkages among ecosystems that occur due to the establishment of non‐native species could be equally disruptive.…”

Multipath ecological influence of an iteroparous fish migration from Lake Biwa to an alluvial stream

“…Both decomposing carcasses of fish (Gende et al, 2007) and excretions from living fish (Vanni, 2002) add ammonium and SRP. Numerous reports have described such fish‐induced increases of ammonium and SRP concentrations in streams (Chaloner et al, 2004, 2007; Collins et al, 2011; Hood et al, 2007, 2019; Johnston et al, 2004; Mitchell & Lamberti, 2005; Moore et al, 2007). The greater number of migratory fish outweighed the dilution effect of the high discharge of the studied stream (1.8 and 3.9 m 3 /s for the north and south distributary, respectively).…”

Climate-Mediated Changes to Linked Terrestrial and Marine Ecosystems across the Northeast Pacific Coastal Temperate Rainforest Margin

“…For instance, persistent soil saturation in the abundant wetlands in the perhumid NPCTR mobilizes DOC and transports it laterally to streams while also increasing anoxic soil conditions that restrict oxidized nutrient forms (e.g., nitrate [NO 3 – ]) in soil water (Emili and Price 2013 , D'Amore et al 2015b ). High biotic demand for nutrients further suppresses inorganic pools (Bisbing and D'Amore 2018 ) and results in organic nutrients as the dominant export to surface waters (Fellman et al 2008 , Hood et al 2019 ). On the other hand, vertical water flow through deep, well-drained soils of the seasonal NCPTR increases DOC sorption onto mineral soil horizons and reduces DOC available for transport to surface waters (Cory et al 2004 ).…”

“…Beyond C, the export of N, P, Fe and other micronutrients is not well quantified for the NPCTR. This is especially true for the thousands of small, ungauged rivers in BC and Alaska, although limited studies suggest that organic N and P yields dominate total N and P export in the north (Hood et al 2019 ). Inorganic nutrient forms dominate N export along the coastal margin from Washington to northern California, which is likely because of local areas of agricultural fertilizer runoff, and more broadly, the abundance of N-fixing alder (Compton et al 2020 ).…”

“…In addition, glacial streams are characterized by high levels of glacier-derived silt and elevated fluxes of rock-derived nutrients such as P and Fe relative to forested watersheds (Hood and Berner 2009 ). Spawning salmon also seasonally release large quantities of inorganic N and P and thereby contribute to seasonal watershed nutrient yields (Hood et al 2019 ). Further effort is needed to constrain nutrient export across space, season, and storm event cycles in the NPCTR (figure 5 ).…”