Lawrence B. Cahoon

Industrialized Animal Production—A Major Source of Nutrient and Microbial Pollution to Aquatic Ecosystems

Livestock production has undergone massive industrialization in recent decades. Nationwide, millions of swine, poultry, and cattle are raised and fed in concentrated animal feeding operations (CAFOs) owned by large, vertically integrated producer corporations. The amount of nutrients (nitrogen and phosphorus) in animal manure produced by CAFOs is enormous. For example, on the North Carolina Coastal Plain alone an estimated 124,000 metric tons of nitrogen and 29,000 metric tons of phosphorus are generated annually by livestock. CAFO wastes are largely either spread on fields as dry litter or pumped into waste lagoons and sprayed as liquid onto fields. Large amounts of nitrogen and phosphorus enter the environment through runoff, percolation into groundwater, and volatilization of ammonia. Many CAFOs are located in nutrient-sensitive watersheds where the wastes contribute to the eutrophication of streams, rivers, and estuaries. There is as yet no comprehensive Federal policy in place to protect the environment and human health from CAFO generated pollutants.

North and South Carolina coasts

Abstract This coastal region of North and South Carolina is a gently sloping plain, containing large riverine estuaries, sounds, lagoons, and salt marshes. The most striking feature is the large, enclosed sound known as the Albemarle–Pamlico Estuarine System, covering approximately 7530 km 2 . The coast also has numerous tidal creek estuaries ranging from 1 to 10 km in length. This coast has a rapidly growing population and greatly increasing point and non-point sources of pollution. Agriculture is important to the region, swine rearing notably increasing fourfold during the 1990s. Estuarine phytoplankton communities in North Carolina are well studied; the most important taxonomic groups are diatoms, dinoflagellates, cryptomonads and cyanobacteria. Several major poorly flushed estuaries are eutrophic due to nutrient inputs, and toxic dinoflagellates ( Pfiesteria spp) can reach high densities in nutrient-enriched areas. Fully marine waters are relatively oligotrophic. Southern species enter in subsurface intrusions, eddies, and occasional Gulf Stream rings, while cool water species enter with the flow of the Labrador Current to the Cape Hatteras region. The Carolinas have a low number of endemic macroalgae, but species diversity can be high in this transitional area, which represents the southernmost extension for some cold-adapted species and the northernmost extension of warm-adapted species. In North Carolina the dominant seagrass, Zostera marina , lies at its southernmost extension, while a second species, Halodule wrightii is at its northernmost extent. Widgeon-grass Ruppia maritima is common, growing in brackish water or low-salinity pools in salt marshes. Seagrass meadows are now much reduced, probably due to elevated nitrogen and increased sedimentation. In sounds, numerically dominant benthic taxa include bivalves, polychaetes and amphipods, many showing gradients in community type from mesohaline areas of the eastern shore to near marine salinities in western parts. The semi-enclosed sounds have extensive shellfisheries, especially of blue crab, northern quahogs, eastern oysters, and shrimp. Problems include contamination of some sediments with toxic substances, especially of metals and PCBs at sufficiently high levels to depress growth of some benthic macroinvertebrates. Numerous fish kills have been caused by toxic Pfiesteria outbreaks, and fish kills and habitat loss have been caused by episodic hypoxia and anoxia in rivers and estuaries. Oyster beds currently are in decline because of overharvesting, high siltation and suspended particulate loads, disease, hypoxia, and coastal development. Fisheries monitoring which began in the late 1970s shows greatest recorded landings in 1978–1982; since then, harvests have declined by about a half. Some management plans have been developed toward improving water quality and fisheries sustainability. Major challenges include; high coliform levels leading to closures of shellfish beds, a problem that has increased with urban development and increasing cover of watershed by impervious surfaces; high by-catch and heavy trawling activity; overfishing which has led to serious declines in many wild fish stocks; and eutrophication. Comprehensive plans limiting nutrient inputs are needed for all coastal rivers and estuaries, not only those that already exhibit problems. There is a critical need to improve management of non-point nutrient runoff through increased use of streamside vegetated buffers, preservation of remaining natural wetlands and construction of artificial wetlands. Improved treatment processes, based on strong incentive programmes, should also be mandated for present and future industrial-scale animal operations.

Alternation of factors limiting phytoplankton production in the Cape Fear River Estuary

Phytoplankton nutrient limitation experiments were performed from 1994 to 1996 at three stations in the Cape Fear River Estuary, a riverine system originating in the North Carolina piedmont. Nutrient addition bioassays were conducted by spiking triplicate cubitainers with various nutrient combinations and determining algal response by analyzing chlorophyll a production and 14C uptake daily for 3 d. Ambient chlorophyll a, nutrient concentration, and associated physical data were collected throughout the estuary as well. At a turbid, nutrient-rich oligohaline station, significant responses to nutrient additions were rare, with light the likely principal factor limiting phytoplankton production. During summer at a mesohaline station, phytoplankton community displayed significant nitrogen (N) limitation, while both phosphorus (P) and N were occasionally limiting in spring with some N+P co-limitation. Light was apparently limiting during fall and winter when the water was turid and nutrient-rich, as well as during other months of heavy rainfall and runoff. A polyhaline station in the lower estuary had clearer water and displayed significant responses to nutrient additions during all enrichment experiments. At this site N limitation occurred in summer and fall, and P limitation (with strong N+P co-limitation) occurred in winter and spring. The data suggest there are two patterns controlling phytoplankton productivity in the Cape Fear system: 1) a longitudinal pattern of decreasing light limitation and increasing nutrient sensitivity along the salinity gradient, and 2) a seasonal alternation of N limitation, light limitation, and P limitation in the middle-to-lower estuary. Statistical analyses indicated upper watershed precipitation events led to increased flow, turbidity, light attenuation, and nutrient loading, and decreased chlorophyll a and nutrient limitation potential in the estuary. Periods of low rainfall and river flow led to reduced estuarine turbidity, higher chlorophyll a, lower ambient nutrients, and more pronounced nutrient limitation.

Sediment Grain Size Effect on Benthic Microalgal Biomass in Shallow Aquatic Ecosystems

Benthic microalgal biomass is an important fraction of the primary producer community in shallow water ecosystems, and the factors controlling benthic microalgal biomass are complex. One possible controlling factor is sediment grain-size distribution. Benthic microalgal biomass was sampled in sediments collected from two sets of North Carolina estuaries Massachusetts and Cape Cod bays, and Manukau Harbour in New Zealand. Comparisons of benthic microalgal biomass and sediment grain-size distributions in these coastal and estuarine ecosystems frequently showed a negative relationship between the proportion of fine-grained sediments and benthic microalgal biomass measured as chlorophylla. The highest sedimentary chlorophylla levels generally occurred in sediments with lower percentages of fine particles (diameter <125 mm). A negative relationship between the proportion of fine sediments and benthic microalgal biomass suggests anthropogenic loadings of fine sediment may reduce the biological productivity of shallow-water ecosystems.

Top down vs. bottom up control of benthic community composition on an intertidal tideflat

Nutrient enrichment and predation have been shown to have important, though sometimes conflicting, effects on intermediate trophic levels in freshwater communities. Though predation is also important in structuring marine soft-sediment benthic communities, the influence of nutrient enrichment in marine benthic systems is less well understood. We examined the interactive effects of nutrient enrichment and predator exclusion on a benthic community to assess the importance of these factors and to test the bottom-up:top-down theory of trophic control in this habitat. Predator exclusion was associated with increased numbers of surface deposit feeders but had less impact on burrowing deposit feeders. Effects of nutrient addition on abundances were observed only in treatments allowing predator access, but increased size of a benthic polychaete, Streblospio benedicti Webster, was observed in predator exclusion treatments with nutrient addition relative to other exclusion plots. However, responses to nutrient addition and predator exclusion varied between years. These results suggest that nutrient addition may be associated with effects on benthic communities, possibly through increased benthic microalgal production, but that the presence or absence of predation may alter the visible response of benthos to enrichment.

Top-down Versus Bottom-up Limitation in Benthic Infaunal Communities: Direct and Indirect Effects

Top-down effects of predators and bottom-up effects related to resource availability can be important in determining community structure and function through both direct and indirect processes. Their relative influence may vary among habitats. We examined the effects of nutrient enhancement and predation in southeastern North Carolina to determine relative effects on benthic macrofaunal communities. Short-term nutrient additions and predator exclusions were conducted in two estuaries to examine main and interactive effects on benthic microalgae and infauna. This experimental approach was complemented by comparisons of microalgal biomass, infaunal abundance and composition, predator abundance and predator exclusion among four estuarine systems that varied in background nutrient levels. In the short-term experiments, nutrient enhancement induced increased microalgal biomass but had limited effects on abundances or sizes of infauna. Predator exclusion increased the density of sedentary and near-surface dwelling fauna, but we did not observe interactions between predation and responses to nutrient additions as might be predicted from a simple cascade model. General patterns of abundance were explained to a larger extent by interannual and amongestuary pattems. These results indicate a lack of simple trophic cascade responses for this community over a short time scale and little evidence for local interactive effects. The lack of interactive effects may reflect the opportunistic nature of the dominant infaunal species and potentially different time and spatial scales for the effects of predation and resource controls.

PHOTOSYNTHETIC AND HETEROTROPHIC IMPACTS OF NUTRIENT LOADING TO BLACKWATER STREAMS

Blackwater stream systems are the most abundant type of freshwater lotic system on the Coastal Plain of the eastern United States. Many of these ecosystems drain watersheds that receive large anthropogenic nutrient inputs, whereas some blackwater systems remain relatively pristine. A series of nutrient addition experiments was carried out over a four-year period to assess the roles of nitrogen and phosphorus loading on the phytoplankton, bacterioplankton, and respiration of two third-order and two fifth-order blackwater streams in southeastern North Carolina. Stream water was distributed into 4-L containers, amended with various nutrient addition treatments, and incubated in gently agitated outdoor pools over a six-day period. Chlorophyll a production, direct bacterial counts, ATP, and biochemical oxygen demand (BOD) were measured as response variables. Significant phytoplankton production over control occurred in most experiments involving nitrogen additions, regardless of whether it was in the form of a...

Benthic microalgal biomass in sediments of Onslow Bay, North Carolina

Abstract Sediment samples were collected at stations along cross-shelf transects in Onslow Bay, North Carolina, during two cruises in 1984 and 1985. Station depths ranged from 11 to 285 m. Sediment chlorophyll a concentrations ranged from 0·06 to 1·87 μg g −1 sediment (mean, 0·55), or 2·6–62·0 mg m 2 . Areal sediment chlorophyll a exceeded water column chlorophyll a a at 16 of 17 stations, especially at inshore and mid-shelf stations. Sediment ATP concentrations ranged from 0 to 0·67 μg g −1 sediment (mean, 0·28). Values for both biomass indicators were lowest in the depth range including the shelf break (50–99 m). Organic carbon contents of the sediments were uniformly low across the shelf, averaging 0·159% by weight. Photography of the sediments revealed extensive patches of microalgae on the sediment surface. Our data suggest that viable benthic microalgae occur across the North Carolina continental shelf. The distribution of benthic macroflora on the North Carolina shelf indicates that sufficient light and nutrients are available to support primary production out to the shelf break. Frequent storm-induced perturbations do not favour settling of phytoplankton, an alternative explanation for the presence of microalgal pigments in the sediments. Therefore, we propose that a distinct, productive benthic microflora exists across the North Carolina continental shelf.

Interactive Effects of Nutrient Additions and Predation on Infaunal Communities

Nutrient additions represent an important anthropogenic stress on coastal ecosystems. At moderate levels, increased nutrients may lead to increased primary production and, possibly, to increased biomass of consumers although complex trophic interactions may modify or mask these effects. We examined the influence of nutrient additions and interactive effects of trophic interactions (predation) on benthic infaunal composition and abundances through small-scale field experiments in 2 estuaries that differed in ambient nutrient conditions. A blocked experimental design was used that allowed an assessment of direct nutrient effects in the presence and absence of predation by epibenthic predators as well as an assessment of the independent effects of predation. Benthic microalgal, production increased with experimental nutrient additions and was greater when infaunal abundances were lower, but there were no significant interactions between these factors. Increased abundances of one infaunal taxa,Laeonereis culveri, as well as the grazer feeding guild were observed with nutrient additions and a number of taxa exhibited higher abundances with predator exclusion. In contrast to results from freshwater systems there were no significant interactive effects between nutrient additions and predator exclusion as was predicted. The infaunal responses observed here emphasize the importance of both bottom-up (nutrient addition and primary producer driven) and top-down (predation) controls in structuring benthic communities. These processes may work at different spatial and temporal scales, and affect different taxa, making observation of potential interactive effects difficult.

Short-term variability of water quality parameters in two shallow estuaries of North Carolina

We quantified the effects of nutrient loading following precipitation events (≥ 1.25 cm) in 2 tidal creeks varying in size and anthropogenic input during the winter and summer seasons of 1996. Several water quality parameters were repeatedly measured in the water column every 3 h for several days after each event (4–5 per season). Total nitrogen (TN) and total phosphorus (TP) behaved nonconservatively with salinity and appeared as pulsed additions, occasionally doubling within 1 to 2 tidal cycles following significant rain events. Average values for TN, TP, and chlorophylla were 10–15 μM, <4 μM, and <7 μg l−1, respectively for winter events and 30–35 μM, >4 μM, and ≥ 7 μg l−1, respectively for summer events. However, response times were variable, depending on the magnitude and duration of the event as well as temperature. Chlorophylla biomass often increased after nutrient additions, especially in the summer when increased nutrient loading took place. Dissolved silica (DSi) behaved conservatively with salinity; low values were observed at high tide and vice versa. Average DSi ranges for winter and summer events were 5–45 μM and 10–85 μM, respectively. DSi range values increased proportionally with the amount of freshwater loaded into the system. Recovery times for salinity were usually greater than the recovery times for nutrients. Dissolved oxygen displayed a diel pattern, increasing after daytime productivity and decreasing during nighttime. In conclusion, each rainfall event was unique and responses were variable depending upon rainfall history, seasonality, and the duration and intensity of the rainfall event. Several other variables, such as water viscosity, percolation rates, and evapotranspiration rates which were not quantified in this study, could have also explained parameter responses.