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

Impervious surfaces have for many years been recognized as an indicator of the intensity of the urban environment and, with the advent of urban sprawl, they have become a key issue in habitat health. Although a considerable amount of research has been done to define impervious thresholds for water quality degradation, there are a number of flaws in the assumptions and methodologies used. Given refinement of the methodology, accurate and usable parameters for preventative watershed planning can be developed, which include impervious surface thresholds and a balance between pervious and impervious surfaces within a watershed.

/pdf/impervious-surfaces-and-water-quality-a-review-of-current-44t2v7vgj3.pdf

Impervious Surfaces and Water Quality: A Review of Current Literature and Its Implications for Watershed Planning

This section is composed of three basic subareas: combined sewer overflows (CSOs), sanitary sewer overflows (SSOs), and stormwater discharges. Much of the literature cited came from documents covering noteworthy global conferences (Bathala, 1996; Engineering Foundation, 1996; Hallam et al., 1996; Maxwell et al., 1996; Sieker and Verworn [Eds.], 1996; Society of Environmental Toxicology and Chemistry, 1996; U.S. EPA 1996a; Water Environment Federation, 1996a,b,c). In addition, the U.S. Environmental Protection Agency (U.S. EPA) published guidance documents (U.S. EPA, 1996,c,d,e), which are discussed in more detail in the subsection Regulatory Policies and Financial Aspects.

https://www.jstor.org/stable/pdfplus/29763265.pdf

Urban wet-weather flows

The southern United States is characterized by a humid, subtropical climate and consists of 16 states (Texas, Oklahoma, Arkansas, Louisiana, Mississippi, Tennessee, Kentucky, Alabama, Florida, Georgia, South Carolina, North Carolina, Virginia, West Virginia, Delaware, and Maryland) and Washington DC. Currently this region is experiencing the largest net population growth in the U.S. Over the last century, the expansion of large urban centers and impervious area in the region has altered the hydrologic cycle. This review synthesizes regional research that shows how watershed hydrology, groundwater recharge, stream geomorphology, climate, biogeochemistry, and stream ecology have been affected by urbanization and the expansion of watershed impervious area.

Urbanization Effects on Watershed Hydrology and In-Stream Processes in the Southern United States

Habitat destruction and fragmentation have been identified as possible causes of large-scale amphibian declines. Here, we examine the effects of adjacent land use and water quality on wetland amphi...

The effects of adjacent land use on wetland amphibian species richness and community composition

This research developed multiple regression models relating land use to in-stream concentrations of total nitrogen (TOTN) and total phosphorus (TOTP) in eight, low-order watersheds on the coastal plain of South Carolina. The study area (4860 km 2 ) included dominant land-use categories of agriculture, forest, urban, and wetland comprising the lower portion of the Lake Marion drainage. Land-use data were obtained from a pre-existing GIS database derived by classification of satellite images. The models partitioned land-use categories according to distance from stream channels using a series of buffer zones around each stream. Effects of point source contributions were removed from observed in-stream concentrations so that nonpoint source effects could be more clearly delineated. All models except two were significant at P 150 m). Land-use change scenarios (converting forest and wetland to agriculture) support the conclusion that management of stream water quality will be most effective with emphasis on riparian and adjacent lands. Seasonal models were generally significant (P < 0.05) and demonstrate that the seasonal profile of stream nutrient concentrations is dependent on the mosaic of land uses in a specific subhasin.

In-Stream Nonpoint Source Nutrient Prediction with Land-Use Proximity and Seasonality

Coastal watersheds in the southeastern United States are rapidly changing due to population growth and attendant increases in residential development, industry, and tourism related commerce. This research examined spatial and temporal patterns of nutrient concentrations in streams from 10 small watersheds (< 4 km2) that drain into Murrells Inlet (impacted) and North Inlet (pristine), two high salinity estuaries along the South Carolina coast. Monthly grab samples were collected during baseflow during 1999 and analyzed for total and dissolved inorganic and organic forms of nitrogen and phosphorus. Data were grouped into forested wetland creeks (representing predevelopment reference sites), urban creeks, and urban ponds. DON and NH4 concentrations were greater in forested streams than in urban streams. NO3 and TP concentrations were greatest in urban streams. Seasonally, concen- trations were highest during summer for TN, NH4, DON, and TP, while NO3 concentrations were greatest during winter. Nutrient ratios clearly highlighted the reduction in organic nitrogen due to coastal development. Multiple regression models to predict instream nutrient concentrations from land use in Murrells Inlet suggest that effects are not significant (small r2). The findings indi- cate that broad land use/land cover classes cannot be used to pre- dict nutrient concentrations in streams in the very small watersheds in our study areas. (KEY TERMS: nonpoint source pollution; urbanization; water qual- ity; watershed management; nutrients; coastal streams.)

James R. Hussey

Papers

In-Stream Nonpoint Source Nutrient Prediction with Land-Use Proximity and Seasonality

Impacts of Urbanization on Nutrient Concentrations in Small Southeastern Coastal Streams