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Coastal & Estuarine Science News (CESN)

Coastal & Estuarine Science News (CESN) is an electronic publication providing brief summaries of select articles from the journal Estuaries & Coasts that emphasize management applications of scientific findings. It is a free electronic newsletter delivered to subscribers on a bimonthly basis.


November 2005

Contents

Balancing Venice's Water Budget: Submarine Groundwater's Role
Good News for the New River
Review Takes Stock of Brown Tide Knowledge
Toxaphene-Contaminated Sediment Remediation Pays Off for GA Fish

Balancing Venice's Water Budget: Submarine Groundwater's Role

The culture and future of Venice, Italy, the so-called "Bride of the Sea," are inextricably tied to water - its sources, movements, and pathways. A 2000 effort to construct a water budget for Venice Lagoon, documenting sources and flows, came up short by at least 15%. This deficit between precipitation and runoff amounts to 2.3 x 106 m3 per year. Recent research has found evidence that the "missing" water input could be accounted for by submarine groundwater discharge (SGD) originating in leakage from deep artesian aquifers. SGD measurements were taken at two sites, a pristine marsh and a bulkheaded industrial site, using benthic chambers made from steel drums fitted with plastic bags for collecting SGD. While SGD varied at both sites with tidal stage (flow was higher at low tide) and spring/neap tides, flows averaged 30 cm d-1 at the marsh site and 6 cm d-1 at the industrialized site. These flow rates, if representative of even a fraction of the lagoon floor, can easily account for the water budget deficit.

Also of note for managers is that ammonium levels were found to be high in the SGD, particularly at the industrial site. Ammonium concentrations increased with rainfall, as did SGD flow at the industrial site, indicating that SGD could be a significant source of contaminants to the lagoon, especially when it rains.

Source: Rapaglia, J. 2005. Submarine groundwater discharge into Venice Lagoon, Italy. Estuaries 28(5): 705-713. (View Abstract)

Good News for the New River

The New River Estuary, NC, is living proof that the deleterious effects of nutrient enrichment can be reversed within a reasonably short time frame if appropriate management actions are taken. It was only 1990 when NOAA issued a report identifying the New as one of the four most eutrophic estuaries in the southeastern U.S. Monthly water quality sampling was conducted between 1995 and 2002, during which time (in 1998) major upgrades to two local wastewater treatment plants were made. The water quality observations revealed a reduction of nitrogen and phosphorus point source inputs to the estuary by 57 and 71%, respectively. Other significant improvements in water quality included overall declines in chlorophyll (69%) and turbidity (31%) and, in the upper estuary, significant decreases in ammonium (an 81% drop), orthophosphate (49%) and chlorophyll (75%). Probably because large reserves of accumulated organic matter still reside in the estuary's sediments, significant increases in dissolved oxygen concentration were rarely observed, although average DO did increase in many areas. A non-significant but encouraging decrease in the number of hypoxic events was also noted.

The authors predict that these improvements will lead to recovery of submerged aquatic vegetation in the estuary, which could be accelerated by focusing restoration efforts on SAV plantings and other habitat improvements. Managers will be heartened that eutrophication can be reversed, but the New is not yet completely renewed: further efforts should focus on the more challenging goal of reducing non-point source nutrient inputs.

Source: Mallin, M. A., M. R. McIver, H. A. Wells, D. C. Parsons and V. L. Johnson. 2005. Reversal of eutrophication following sewage treatment upgrades in the New River Estuary, North Carolina. Estuaries 28(5): 750-760. (View Abstract)

Review Takes Stock of Brown Tide Knowledge

Since the first recorded brown tides turned the waters of Rhode Island and New York's coastal embayments coffee-brown in the summer of 1985, much has been learned about the dynamics of these devastating harmful algal blooms (HABs) and the biology and ecology of the bloom organism, Aureococcus anophagefferens. A review article in Estuaries summarizes much of the brown tide research conducted in the past two decades, and provides suggestions for promising bloom mitigation and control options. A sampling of what is known so far: Unlike most HABs, brown tide does not occur in response to inorganic nutrient loading. Instead, it thrives on dissolved organic nitrogen and other organic nutrients, outcompeting other algal species when organic nutrients are high and inorganic nutrients are low. Blooms tend to form in shallow estuaries with long residence times, and are associated with high salinities and low light conditions.

Since its appearance in the northeast twenty years ago brown tide has spread (or at least been identified further afield from the first bloom sites): blooms have occurred as far south as Virginia, and across the Atlantic in South Africa. How can these blooms, so damaging to ecosystems and economies, be controlled? While there aren't many options, some of the current knowledge about the blooms helps identify the most promising management avenues. Because the blooms tend to form in places with restricted circulation, one (likely controversial) option would be to dredge channels to increase circulation in those areas. Restoration of shellfish beds to increase grazing on the brown tide alga would probably help, since adult bivalves seem less susceptible to the effects of brown tide than larvae and juveniles. Finally, tight nutrient controls might help in the long run (while, ironically, restrictions on inorganic nutrients may lead to dominance of the nutrient pool by organic nutrients, favoring blooms in the short term). While the use of clay as a flocculent has been shown to successfully remove some other HAB cells from the water column, this approach is not recommended for brown tide both because laboratory experiments have indicated the success of this approach with A. anophagefferens is limited and because the clay may have other unintended impacts on the estuary.

Source: Gobler, C. J., D. J. Lonsdale, and G. L. Boyer. 2005. A review of the causes, effects and potential management of harmful brown tide blooms caused by Aureococcus anophagefferens (Hargraves et Sieburth). Estuaries 28(5): 726-749. (View Abstract)

Toxaphene-Contaminated Sediment Remediation Pays Off for GA Fish

Removal of sediments from estuarine sites contaminated with organic pollutants can be a contentious and complex solution to a serious problem - just ask anyone working in the Hudson River watershed. But dredging contaminated sediments has often been shown to effectively reduce contaminant concentrations in edible fish tissue. A new case in point is the reduction of levels of toxaphene (a pesticide compound) in fish sampled before and after remedial action in tidal creeks near the plant in Brunswick, GA where toxaphene was manufactured from 1948 to 1980. Before the 1999 remediation, a 1997 survey conducted by the Georgia Department of Natural Resources found toxaphene levels in finfish of up to 20 μg/g, well above the levels considered safe for human consumption. The authors of the current study used the same protocols to look for toxaphene in fish tissue in the same creeks in 2001, and found that although toxaphene levels remained elevated in fish closest to the source, average lipid-normalized toxaphene levels were significantly reduced (up to 62%) between the two collections. Some species-specific patterns emerged. Benthic feeders such as spot and mullet exhibited higher toxaphene levels than other species, and the species that use the estuary only as a wintering ground (kingfish, seatrout), finding shelter but not feeding, were lower in toxaphene than those that gorged themselves in the warm summer months.

These results provide the first evidence that reduction of toxaphene residues in sediments can lead to concomitant declines in fish tissue concentrations. The authors speculate that further reductions may yet occur, leading to changes in fish consumption advisories for the region.

Source: Maruya, K. A., L. Francendese, and R. O. Manning. 2005. Residues of toxaphene decrease in estuarine fish after removal of contaminated sediments. Estuaries 28(5): 786-793. (View Abstract)