1. Pacific salmon (Oncorhynchus spp.) deliver salmon-derived nutrients (SDN) to the streams in which they spawn. However, many stream parameters, such as discharge and spawner abundance, can vary from year to year, which could alter the quantity and flux of SDN. 2. Over six consecutive years, we studied responses in streamwater chemistry and epilithon (i.e. the microbial community on submerged rocks) to salmon spawners in Fish Creek, southeastern Alaska, U.S.A. The lower reach of Fish Creek receives spawners of several salmon species, while the upper reach does not receive spawners because of an intervening waterfall. 3. We estimated salmon spawner biomass, analysed water chemistry [ammonium, nitrate, soluble reactive phosphorus (SRP) and dissolved organic carbon (DOC)], and measured epilithon abundance [as chlorophyll a (chl a) and ash-free dry mass (AFDM)] in Fish Creek. Measurements were made in both the upper and lower reaches, before, during and after the major salmon runs. 4. Absolute values and relative differences indicated that the presence of salmon spawners consistently increased dissolved ammonium (by 58 lg L )1 on average, 41· over background), SRP (by 6 lg L )1 , 14·), epilithon chl a (by 35 mg m )2 , 16·), and epilithon AFDM (by 3 g m )2 , 8·). Salmon spawners did not increase nitrate or DOC in either absolute or relative amounts. The persistence and magnitude of spawner effects varied among years and appeared to reflect weather-driven hydrology as well as spawner biomass. 5. Salmon-derived nutrients can stimulate the growth of primary producers by increasing streamwater nutrient concentrations, but this positive influence may be modulated by other factors, such as water temperature and discharge. To better assess the ecological influence of SDN on stream biota, future studies should explicitly consider the role of key environmental factors and their temporal and spatial dynamics in stream ecosystems.

Metrics can inform investors wary of “green washing”

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Spawning migrations of Pacific salmon (Oncorhynchus spp.) represent a significant nutrient pulse to freshwater ecosystems of southeastern Alaska. These salmon-derived nutrients (SDN) can be transported by streamflow from spawning reaches of streams to estuaries, where their fate and significance have not been studied. Such estuaries represent an important aquatic ecotone in southeastern Alaska, especially for juvenile salmonids. We sampled dissolved nutrients and epilithon (i.e., benthic algae attached to rocks) before, during, and after salmon runs in three Alaskan streams and their associated estuaries. Salmon runs increased streamwater fluxes of dissolved ammonium and soluble reactive phosphorus to estuaries by 30 -350 % and 14 -130 %, respectively, depending on the stream and period. Although epilithon chlorophyll a and biomass increased in streams in response to SDN, epilithon did not increase in associated estuaries. We suggest that salmon spawner disturbance during estuary reddbuilding, invertebrate grazing, physical transitions from summer to fall, and nutrient influx from nutrient-rich tidal flow may have limited epilithon growth responses to SDN in estuaries. Although estuaries receive a significant flux of SDN flushed downstream from freshwaters, epilithon does not measurably respond to this nutrient enrichment from spawning salmon.

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Expansion of agriculture in the Brazilian Amazon has been driven not just by demands from traditional, rural producers, but also large agriculture and cattle producers, both of whom have put considerable pressure on remaining forests and their watersheds. Monitoring of these watersheds has been a focus of intensive study for the past 20 years and although this work has greatly increased our understanding, considerable gaps still remain in our ability to provide adequate recommendations for land management and associated public policies. In this study we present a summary of findings from these previous results. For small properties, the use of fire to prepare land for cultivation remains controversial, while in large properties, forest conversion to pasture and/or crop production has had a meaningful and adverse effect on water quality. Riparian forest conservation can make a significant difference in reducing impacts of land-use change. Secondary vegetation can also play an important role in mitigating these impacts. New types of sustainable agricultural production systems, together with incentives such as payments for ecosystem service can also contribute. Continued monitoring of these changes, together with robust sustainable development plans, can help to preserve forest while still addressing the social and economic needs of Amazonian riverine inhabitants.