After a pollution source is removed from a coastal area, how quickly does the impacted area recover? One study in an Argentinean bay suggests that recovery, at least from the perspective of cellular genetics, can be swift.
The investigators used micronuclei (MN) frequencies in mussel species as an indicator of genetic damage done to the bivalves by sewage pollution. Mussels were gathered from a site impacted by sewage sludge discharge both before and after cessation of the discharge, as well as from pollution-impacted and pristine control sites, in Puerto Madryn, Argentina. Micronuclei form in genetically damaged tissue when small lengths of chromosome break off during cell-division; evaluation of MN frequencies is a simple, low-cost way of determining cytogenetic damage.
MN frequencies were lowest in the pristine site, higher in the pollution-impacted control site, and higher still in the sewage impacted site. Within six months of cessation of sewage sludge dumping, MN frequencies at the test site had declined significantly, from a mean MN frequency of 11.58 to 2.29 per 1,000 cells. After a year, the MN frequency at the test site was not significantly different than that at the pristine site. Water quality, as measured by dissolved oxygen, biological oxygen demand, and phosphorous concentration, also improved significantly at the test site.
This rapid recovery provides evidence that this type of site could eventually be used for activities such as bivalve aquaculture, although other indicators of environmental quality such as contaminant concentrations would also need to be evaluated.
Source: Machado-Schiaffino, G., L. O. Bala, and E. Garcia-Vazquez. 2009. Recovery of normal cytogenetic records in mussels after cessation of pollutant effluents in Puerto Madryn (Patagonia, Argentina). Estuaries and Coasts 32 (DOI 10.1007/s12237-009-9173-9).
Altering freshwater flows into estuarine nursery areas is one of the key ways in which development of watersheds can contribute to habitat degradation. The increase in paved surfaces and concomitant decrease in wetlands and other natural habitats can alter the source, timing, and velocity of freshwater flows, thus influencing salinity patterns. Some species’ adaptation to limited salinity ranges or specific temporal patterns in salinity and flow means that these changes can be a problem. For example, a study in four southwest Florida creeks in the Charlotte Harbor watershed indicates that alteration of freshwater flow has impacted juvenile snook feeding habits and trophic ecology.
The researchers examined juvenile snook stomach contents and used stable isotope analysis to examine fish diets and trophic status in “less degraded” and “more degraded” mangrove creeks. The more degraded creek watersheds had extensive upland development which altered flow regimes, causing short hydroperiods, scouring, and reduced salinities. The diets of the fish caught in the less degraded creeks was more diverse than those of fish in the more degraded creeks. Total number of prey items was twice as high in the less degraded sites, and total weight of prey was higher as well. Stable isotope analysis suggested greater inter-individual diet variation in snook taken from the less degraded sites, and consequently dependence on a few dominant prey items in the more degraded creeks. These results also indicated that a fundamental shift in the food web has taken place following human alteration of freshwater flows in these systems.
Although more research is needed to fully link the observed changes in diet to growth and survival and ultimately to recruitment, managers should note that 25% of US coastal habitats are expected to be developed by the year 2025. More flow alteration, and other anthropogenic impacts, are likely to be on the way.
Source: Adams, A. J., R. K. Wolfe, and C. A. Layman. 2009. Preliminary examination of how human-driven freshwater flow alteration affects trophic ecology of juvenile snook (Centropomus undecimalis) in estuarine creeks. Estuaries and Coasts 32 (DOI 10.1007/s12237-009-9156-x).
Eutrophication is one of the most serious problems faced by estuarine and coastal ecosystems. To address it, controls on nutrient loadings are clearly needed, but which nutrients? Decades of research have confirmed that phosphorous is limiting in freshwater systems. In response to that information, management steps have been taken all over the world to limit P loading to freshwater ecosystems, with often remarkable results.
In coastal waters, nitrogen has historically been considered the limiting nutrient, in part because while P is “trapped” in receiving waters, N is fixed and lost to the atmosphere. However, anthropogenic phenomena affecting both sides of the N:P ratio have combined to increase that ratio in coastal waters: Human activities have contributed an overabundance of nitrogen loadings to these ecosystems, while upstream nutrient controls focusing exclusively on removing P have also increased downstream N/P ratios. In a 2008 paper in the Proceedings of the National Academy of Science, it was suggested that effective eutrophication control can be achieved in both freshwater and coastal ecosystems by controlling P only, based on research done in an experimental lake. The conclusion of the 2008 paper was that because N2 fixation can respond to meet ecosystem N requirements in a regime of P enrichment, P ultimately controls eutrophication and there is no pressing need for N input controls. A paper appearing in a recent issue of Estuaries and Coasts questions this finding. Evidence is presented that both N and P must be reduced to battle eutrophication in coastal waters. The Estuaries and Coasts paper points out that nutrient dynamics in coastal and estuarine waters are quite different from those in freshwater systems such as the experimental lake described in the 2008 paper. For example, because it controlled by a wide array of physical-chemical and biotic processes, estuarine and coastal N2 fixation generally does not satisfy ecosystem-level N demands, causing these waters to remain N-limited and hence sensitive to N over-enrichment. Furthermore, upstream nutrient management actions such as removal of P alone have exacerbated N-limited downstream eutrophication. The author emphasizes that control of both N and P is needed for long-term management of eutrophication in both types of systems.
Source: W Paerl, H.. 2009. Controlling eutrophication along the freshwater-marine continuum: Dual nutrient (N and P) reductions are essential. Estuaries and Coasts 32 (DOI 10.1007/s12237-009-9158-8).
Schindler, D.W., R.E. Hecky, D.L. Findlay, M.P. Stainton, B.R. Parker, M. Paterson, K.G. Beaty, M. Lyng, and S.E.M. Kasian. 2008. Eutrophication of lakes cannot be controlled by reducing nitrogen input: Results of a 37 year whole ecosystem experiment. Proceedings of the National Academy of Science USA 105: 11254–11258. DOI: 10.1073/pnas.0805108105.
Additional Information: For another response to the PNAS article, see Conley, D. J, H. W. Paerl, R. W. Howarth, D. F. Boesch, S. P. Seitzinger, K. E. Havens, C. Lancelot, & G. E. Likens. 2009. Controlling eutrophication: Nitrogen and phosphorus. Science 323: 1014-1015.
The SeaWiFS satellite mission has been ongoing for about ten years, collecting images of the ocean which can be transformed into valuable data about chlorophyll concentrations. A wealth of information relevant for science and management at large spatial scales can be gained from examination of these dynamic maps. A recent paper discusses the wide range of potential uses of these data, providing examples of useful indicators derived from the data for the northwest Atlantic and offering guidelines to those that might want to utilize this unique treasure trove. Combining the SeaWiFS data with sea surface temperatures taken from another satellite monitoring program (NOAA/NASA AVHRR Pathfinder), the authors examined trends in 19 indicators, including the start, duration, and amplitude of spring and fall phytoplankton blooms, phytoplankton productivity, size structure of the algal cells, and presence of diatoms in blooms. The most pronounced signal in the data is the seasonality of phytoplankton concentrations, characterized by a strong bloom in the spring and a weaker one in the fall. The authors note a high degree of interannual variability in the phenology of these blooms, which could be of critical importance to the survival of larval fish. Variations were also observed in the amplitude and duration of the blooms. The data indicate that this large region can be divided into four ecological provinces (polar boreal, Arctic, NW Atlantic shelf, north Atlantic drift) whose boundaries fluctuate somewhat with variations in physical forcing factors.
The massive amount of data provided by SeaWiFS in the past ten years is a boon to researchers, but it could also be an obstacle: The mass of data is indigestible unless steps are taken to consolidate and average the information appropriately. The authors warn that data averaging can be misleading if it is carried out over more than one of the four ecological provinces. However, “too much data” is a good problem for scientists and managers to have, as long as data averaging is done carefully.
Source: Platt, T., S. Sathyendranath, G. N. White III, C. Fuentes-Yaco, L. Zhai, E. Devred, and C. Tang. 2009. Diagnostic properties of phytoplankton time series from remote sensing. Estuaries and Coasts 32 (DOI 10.1007/s12237-009-9161-0).