Removal of nutrients in various types of constructed wetlands.

Rates and reactions of biogeochemical processes vary in space and time to produce both hot spots and hot moments of elemental cycling. We define biogeochemical hot spots as patches that show disproportionately high reaction rates relative to the surrounding matrix, whereas hot moments are defined as short periods of time that exhibit disproportionately high reaction rates relative to longer intervening time periods. As has been appreciated by ecologists for decades, hot spot and hot moment activity is often enhanced at terrestrial-aquatic interfaces. Using examples from the carbon (C) and nitrogen (N) cycles, we show that hot spots occur where hydrological flowpaths converge with substrates or other flowpaths containing complementary or missing reactants. Hot moments occur when episodic hydrological flowpaths reactivate and/or mobilize accumulated reactants. By focusing on the delivery of specific missing reactants via hydrologic flowpaths, we can forge a better mechanistic understanding of the factors that create hot spots and hot moments. Such a mechanistic understanding is necessary so that biogeochemical hot spots can be identified at broader spatiotemporal scales and factored into quantitative models. We specifically recommend that resource managers incorporate both natural and artificially created biogeochemical hot spots into their plans for water quality management. Finally, we emphasize the needs for further research to assess the potential importance of hot spot and hot moment phenomena in the cycling of different bioactive elements, improve our ability to predict their occurrence, assess their importance in landscape biogeochemistry, and evaluate their utility as tools for resource management.

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Biogeochemical Hot Spots and Hot Moments at the Interface of Terrestrial and Aquatic Ecosystems

Wetlands and streams buffer the interactions among uplands and adjacent aquatic systems. Phosphorus (P) is often the key nutrient found to be limiting in both estuarine and freshwater ecosystems. As such, the ability of wetlands and streams to retain P is key to determining downstream water quality. This article reviews the processes and factors regulating P retention in streams and wetlands and evaluates selected methodologies used to estimate P retention in these systems. Phosphorus retention mechanisms reviewed include uptake and release by vegetation, periphyton and microorganisms; sorption and exchange reactions with soils and sediments; chemical precipitation in the water column; and sedimentation and entrainment. These mechanisms exemplify the combined biological, physical, and chemical nature of P retention in wetlands and streams. Methodologies used to estimate P retention include empirical input-output analysis and mass balances, and process kinetics applied at various scales, including micro- a...

/pdf/phosphorus-retention-in-streams-and-wetlands-a-review-1tz9yqefze.pdf

Phosphorus Retention in Streams and Wetlands: A Review

https://www.jstor.org/stable/10.1641/0006-3568(2001)051%5B0373:RNLTTG%5D2.0.CO;2

Reducing Nitrogen Loading to the Gulf of Mexico from the Mississippi River Basin: Strategies to Counter a Persistent Ecological Problem

Water quality in many stream catchments and river basins is severely impacted by nutrient enrichment as a result of agriculture. Water-resource managers worldwide are considering the potential role of riparian zones and floodplain wetlands in improving stream-water quality, as there is evidence at the site scale that such wetlands are efficient at removing nutrients from through-flowing water. However, recent studies have highlighted disadvantages of such use of wetlands, including emissions of greenhouse gases and losses of biodiversity that result from prolonged nutrient loading. Here, we discuss the water purification function of wetlands at the site and catchment scale and suggest ways in which these disadvantages could be overcome.

https://www.cell.com/trends/ecology-evolution/pdf/S0169-5347(05)00378-2.pdf

Regional and global concerns over wetlands and water quality

Freshwater wetlands alter surface water quality in ways which benefit downstream use. This review summarizes the mechanisms of freshwater wetland interaction with sediment and nutrients that affect surface water quality. The mechanisms vary in magnitude and reversibility, and differ among wetland types. They include sedimentation, plant uptake, litter decomposition, retention in the soil, and microbial processes. Sedimentation is a relatively permanent retention mechanism whereby particulates and associated contaminants are physically deposited on the wetland soil surface. Plant uptake and litter decomposition provide short‐to long‐term retention of nutrients, depending on rates of leaching, translocation to and from storage structures, and the longevity of plant tissues. Plant litter can also provide a substrate for microbial processing of nutrients. Wetland soils sorb nutrients, and provide the environment for aerobic and anaerobic microorganisms that process nutrients. Wetland storage compartm...

C.A. Johnstone

Papers

Sediment and nutrient retention by freshwater wetlands: effects on surface water quality