Matthew R. McIver

Demographic, landscape, and meteorological factors controlling the microbial pollution of coastal waters

Coastal areas in the United States and many other countries are considered to be desirable regions to live and recreate. However, as human use of coastal land and water increases, so does the incidence of aquatic-borne disease from contact with contaminated water and eating contaminated shellfish. Movement of humans into coastal areas both greatly increases the number of sources of microbial pathogens and radically alters the landscape through increased construction activity and paving of former natural areas. On a regional scale, increases in human population over a 14-year period in coastal North Carolina were strongly correlated with increases in shellfish bed closures due to high fecal coliform bacterial counts. On a watershed scale, an analysis of several tidal creeks found strong correlations between mean estuarine fecal coliform bacterial counts and watershed population, percent developed area and especially with percent impervious surface coverage. Conversion of natural landscapes to impervious surfaces (roads, drives, sidewalks, parking lots and roofs) removes the lands natural filtration capability, allows for increased concentration of pollutants at the lands surface and provides a means of rapid conveyance of pollutants to downstream waterways. An analysis of rural watersheds in the Coastal Plain found that stream fecal coliform counts and turbidity were both strongly correlated with rainfall in the previous 24 h in watersheds containing extensive industrial swine and poultry operations, as well as watersheds containing more traditional agriculture and cattle husbandry. In contrast, in watersheds rich in swamp wetlands these relationships were not significant, even in watersheds containing extensive animal production. Based on these findings, we suggest that waterborne microbial pathogen abundance can be minimized in urbanizing coastal areas through reduced use of impervious surfaces and maximal use of natural or constructed wetlands for passive stormwater runoff treatment. In animal husbandry areas, retention of natural wetlands and management practices designed to minimize sediment runoff can likely reduce inputs of pathogenic microbes into streams.

HURRICANE EFFECTS ON WATER QUALITY AND BENTHOS IN THE CAPE FEAR WATERSHED: NATURAL AND ANTHROPOGENIC IMPACTS

In the summer of 1996, southeastern North Carolina, United States, was struck by two hurricanes, with the second (Hurricane Fran) doing considerably more damage than the first (Hurricane Bertha). The Cape Fear watershed, largest in North Carolina, suffered from severe water quality problems for weeks following Fran, including a massive fish kill in the Northeast Cape Fear River. Post-hurricane flooding caused inputs of riparian swamp water to river channels, and sewage treatment plant and pump station power failures caused diversions of millions of liters of raw and partially treated human waste into rivers. Additionally, several swine waste lagoons were breached, overtopped, or inundated, discharging large quantities of concentrated organic waste into the system, particularly into the Northeast Cape Fear River. Dissolved oxygen (DO) decreased to 2 mg/L in the mainstem Cape Fear River, and fell to zero in the Northeast Cape Fear River for >3 wk. Biochemical oxygen demand in the Northeast Cape Fear River w...

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.

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...

Reversal of Eutrophication Following Sewage Treatment Upgrades in the New River Estuary, North Carolina

The New River Estuary consists of a series of broad shallow lagoons draining a catchment area of 1,436 km2, located in Onslow County, North Carolina. During the 1980s and 1990s it was considered one of the most eutrophic estuaries in the southeastern United States and sustained dense phytoplankton blooms, bottom water anoxia and hypoxia, toxic outbreaks of the dinoflagellatePfiesteria, and fish kills. High nutrient loading, especially of phosphorus (P), from municipal and military sewage treatment plants was the principal cause leading to the eutrophic conditions. Nutrient addition bioassay experiments showed that additions of nitrogen (N) but not P consistently yielded significant increases in phytoplankton production relative to controls. During 1998 the City of Jacksonville and the U.S. Marine Corps Base at Camp Lejeune completely upgraded their sewage treatment systems and achieved large improvements in nutrient removal, reducing point source inputs of N and P to the estuary by approximately 57% and 71%, respectively. The sewage treatment plant upgrades led to significant estuarine decreases in ammonium, orthophosphate, chlorophylla, and turbidity concentrations, and subsequent increases in bottom water dissolved oxygen (DO) and light penetration. The large reduction in phytoplankton biomass led to a large reduction in labile phytoplankton carbon, likely an important source of biochemical oxygen demand in this estuary. The upper estuary stations experienced increases in average bottom water DO of 0.9 to 1.4 mg l−1, representing an improvement in benthic habitat for shellfish and other organisms. The reductions in light attenuation and turbidity should also improve the habitat conditions for growth of submersed aquatic vegetation, an important habitat for fish and shellfish.

Nutrient limitation and algal blooms in urbanizing tidal creeks

Abstract Tidal creeks are commonly found in low energy systems on the East and Gulf Coasts of the United States, and are often subject to intense watershed human development. Many of these creeks are receiving urban and suburban runoff containing nutrients, among other pollutants. During the period 1993–2001, we studied three tidal creeks located in southeastern North Carolina, a rapidly urbanizing area. All three creeks received anthropogenic nutrient loading. Oligohaline to mesohaline stations in upper tidal creek regions had much higher nutrient (especially nitrate–N) concentrations than lower creek areas, and hosted spring and summer phytoplankton blooms that at times exceeded 200 μg chlorophyll a l −1 . Phytoplankton biomass during winter was low at all stations in all three creeks. Spring and summer nutrient addition bioassay experiments were conducted to characterize the nutrients limiting phytoplankton growth. Water from high salinity stations in all three creeks always showed significant positive responses to nitrate–N inputs, even at concentrations as low as 50 μg N l −1 . Low salinity stations in upper creek areas often showed significant responses to nitrate–N inputs, but on occasion showed sensitivity to phosphorus inputs as well, indicating the influence of anthropogenic nitrate loading. During several experiments, one of the upper stations showed no positive response to nutrient inputs, indicating that these stretches were nutrient replete, and further phytoplankton growth appeared to be light-limited either by phytoplankton self-shading or turbidity. Water from upper creek areas yielded much higher chlorophyll a concentrations in bioassay experiments than did lower creek water. In general, these urbanizing tidal creeks were shown to be very sensitive to nitrogen loading, and provide a physical environment conducive to phytoplankton bloom formation in nutrient-enriched areas. Tidal creeks are important ecological resources in that they are considered to be nursery areas for many species of fish and shellfish. To protect the ecological function of these small, but very abundant estuarine systems, management efforts should recognize their susceptibility to algal blooms and focus on control of nonpoint source nutrient inputs, especially nitrogen.

Microcystins and two new micropeptin cyanopeptides produced by unprecedented Microcystis aeruginosa blooms in North Carolina's Cape Fear River

The Cape Fear River is the largest river system in North Carolina. It is heavily used as a source of drinking water for humans and livestock as well as a source of irrigation water for crops, and production water for industry. It also serves as a major fishery for both commercial and recreational use. In recent years, possibly related to increased eutrophication of the river, massive blooms of cyanobacteria, identified as Microcystis aeruginosa have been observed. Bloom samples collected in 2009 and 2012 were chemically analyzed to determine if they contained cyanobacterial toxins known as microcystins. Both blooms were found to produce microcystins in high yields. Microcystins are potent hepatotoxins that can be bio-accumulated in the food chain. Recent biological studies have also shown a host of other potentially harmful effects of low level microcystin exposure. Detailed chemical analysis of these blooms led us to discover that these blooms produce an additional family of cyanobacterial peptides know as the micropeptins, including two new members named micropeptins 1106 and 1120. The biological activities of these new molecules have not yet been determined, although protease activity has been well documented for this peptide group. These data indicate a need for thorough monitoring of toxin levels especially during bloom events in addition to additional biological testing of other cyanopeptides present in blooms.

Elevated levels of metals and organic pollutants in fish and clams in the Cape Fear River watershed.

A study was performed in 2003 to 2004 to assess metal and organic contaminant concentrations at three areas in the lower Cape Fear River system, North Carolina, United States. Sites examined were Livingston Creek along the mainstem of the Cape Fear River near Riegelwood, Six Runs Creek in the Black River Basin, and Rockfish Creek in the Northeast Cape Fear River basin. The results of the investigation showed that levels of metals and organic pollutants in the sediments were lower than limits considered harmful to aquatic life. However, results of fish (adult bowfin) tissue analyses showed that concentrations of arsenic (As), cadmium (Cd), mercury (Hg), selenium (Se), and now-banned polychlorinated biphenyls (PCBs), and the pesticide dieldrin were higher than levels considered safe for human consumption by the United States Environmental Protection Agency and the North Carolina Health Director’s Office. Fish tissue concentrations of Hg, Se, and PCBs were also higher than concentrations determined by researchers to be detrimental either to the health of the fish themselves or their avian and mammalian predators. Due to the rural nature of two of the sites, increased concentrations of As, Cd, Se, and PCBs in fish tissue were unexpected. The likely reason the levels are increased in fish and some clams but not in sediments is that these pollutants are biomagnified in the food chain. These pollutants will also biomagnify in humans. In these rural areas there is subsistence fishing by low-income families; thus, increased fish tissue metals and toxicant concentrations may present a direct threat to human health.

Pollutant impacts to Cape Hatteras National Seashore from urban runoff and septic leachate

The sandy barrier islands of Cape Hatteras National Seashore, USA, attract large seasonal influxes of tourists, and are host to numerous motels, rentals and second homes. To investigate the impacts of nearby urbanization on public trust waters, sampling was conducted in nine brackish water bodies within this coastal national park. A large tidal urban ditch delivered runoff-driven fecal-contaminated water directly into public beach waters. At all sites except the control, ammonium, phosphorus and fecal bacteria concentrations were high, strongly seasonal and significantly correlated with community water usage, indicating that increased septic tank usage led to increased pollutant concentrations in area waterways. Nutrients from septic systems caused ecosystem-level problems from algal blooms, BOD, and hypoxia while fecal microbes created potential human health problems. Septic system usage is widespread in sensitive coastal areas with high water tables and sandy soils and alternatives to standard septic systems must be required to protect human health and the environment.

High pollutant removal efficacy of a large constructed wetland leads to receiving stream improvements.

Hewletts Creek, in Wilmington, North Carolina, drains a large suburban watershed and as such is affected by high fecal bacteria loads and periodic algal blooms from nutrient loading. During 2007, a 3.1-ha wetland was constructed to treat stormwater runoff from a 238-ha watershed within the Hewletts Creek drainage. A rain event sampling program was performed in 2009-2010 to evaluate the efficacy of the wetland in reducing pollutant loads from the stormwater runoff passing through the wetland. During the eight storms sampled, the wetland greatly moderated the hydrograph and retained and/or removed 50 to 75% of the inflowing stormwater volume. High removal rates of fecal coliform bacteria were achieved, with an average load reduction of 99% and overall concentration reduction of >90%. Particularly high (>90%) reductions of ammonium and orthophosphate loads also occurred, and lesser but still substantial reductions of total phosphorus (89%) and total suspended solids loads (88%) were achieved. Removal of nitrate was seasonally dependent, with lower removal occurring in cold weather and a high percentage (90%+) of nitrate load removal occurring in the growing season when water temperature exceeded 15°C. Long-term before-and-after sampling in downstream Hewletts Creek proper showed that, after wetland construction, statistically significant average decreases of 43% for nitrate, 72% for ammonium, and 59% for fecal coliform bacteria were realized. Wetland features contributing to the high pollutant control efficacy included available space for a large wetland, construction of deep forebays, and a dense and diverse aquatic and shoreline plant assemblage.