and nutrient fluxes through the hyporheic zone (area between surface water and groundwater) of rivers and effects the dispersion and retention of marine derived nutrients (MDN) within the river ecosystem. MDN are delivered to river and stream ecosystems by the fecal matter of spawning salmon and the decaying carcasses of salmon that have completed spawning and died. Numerical modeling suggests that residence time of MDN within a salmon spawning reach is inversely proportional to the amount of redd construction within the river. Measurements of respiration within a salmon-bearing river in Alaska further suggest that salmon bioturbation of the river bed plays a significant role in mobilizing MDN and limiting primary productivity while salmon spawning is active. The river ecosystem was found to switch from a net autotrophic to heterotrophic system in response to decreased primary production and increased respiration. The decreased primary production in this study was attributed to the loss of benthic primary producers who were dislodged due to bioturbation, while increased respiration was thought to be due to increased respiration of organic carbon, also attributed to sediment mobilization from salmon redd construction. While marine derived nutrients are generally thought to increase productivity in riparian and freshwater ecosystems, several studies have suggested that temporal effects of bioturbation should be considered when characterizing salmon influences on nutrient cycles. Marine environments Major marine bioturbators range from small infaunal invertebrates to fish and marine mammals. In most marine sediments, however, they are dominated by small invertebrates, including polychaetes, bivalves, burrowing shrimp, and amphipods. Shallow and Coastal Coastal ecosystems, such as estuaries, are generally highly productive, which results in the accumulation of large quantities of detritus (organic waste). These large quantities, in addition to typically small sediment grain size and dense populations, make bioturbators important in estuarine respiration. Bioturbators enhance the transport of oxygen into sediments through irrigation and increase the surface area of oxygenated sediments through burrow construction. Bioturbators also transport organic matter deeper into sediments through general reworking activities and production of fecal matter. This ability to replenish oxygen and other solutes at sediment depth allows for enhanced respiration by both bioturbators as well as the microbial community, thus altering estuarine elemental cycling. The effects of bioturbation on the nitrogen cycle are well-documented. Coupled denitrification and nitrification are enhanced due to increased oxygen and nitrate delivery to deep sediments and increased surface area across which oxygen and nitrate can be exchanged.