Changes in water quality and plankton of Kingston Harbour, Jamaica, after 20 years of continued eutrophication
Organic pollution of Kingston Harbour has continued unabated since the first set of comprehensive studies (conducted in the 1970s), which indicated that the area was under stress. The major objective of the most recent study (concluded in the 1990s) was, therefore, to investigate the changes in the water quality and planktonic communities of Kingston Harbour after 20 yrs of continuous nutrient loading. To this end, the abundance, species composition and community structure of the planktonic communities were examined along with water column temperature, salinity, dissolved oxygen, NO2-N + NO3-N and PO4-P concentrations between December 1993 and February 1995 (inclusive). The indices used were similar to those used in the previous characterization and only stations common to both studies and sampled over the entire annual cycle were used for the comparison. All physico-chemical parameters examined (with the exception of light extinction and phosphates) were significantly different between the two studies especially the nitrite + nitrate concentration. Maximum labile NO2-N + NO3-N concentration of 45.3 μM and maximum PO4-P concentration of 0.95 μM were recorded in the 1994 study compared with values in the 1972 data of 2.02 μM and 1.49 μM, respectively. The increased eutrophic state was indicated by the significantly higher values for mean phytoplankton abundance throughout the harbor compared to 1973 findings. Mean phytoplankton abundance (29 × 107 cells L−1) for the entire harbor was higher than the previous maximum (5 × 107 cells L−1). Phytoplankton biomass values were also significantly higher (maximum average = 26.1 mg m−3 chlorophyll a) compared to previous findings (maximum average = 16.82 mg m−3) and followed distribution patterns similar to abundance values. The impact of continued eutrophication is further evidenced in a shift in phytoplankton community composition during the 20 yrs from dominance of smaller cells and diatoms to a dominance of larger cells and dinoflagellates. In the 1994, mean total numbers of zooplankton for the area were significantly higher and ranged from 3347 animals m−3 in Hunts Bay to 91,905 animals m−3 at station 8, located at the end of the airport runway. This maximum value was 3.6 times the maximum reported in the 1972 study (25,248 animals m−3), but it was obtained at the same station. In fact, for all zooplankton indices except Paracalanus spp. and Lucifer faxoni numbers, the values in the present study were all on average between 5.5–1.2 times greater than in 1972. They also followed a similar pattern of distribution. Obvious differences in species distribution were seen in Temora turbinata numbers, which in the present study were far more important (on average 52 times greater) than in the earlier study, and in Penilia avirostris, which dominated the harbor in the 1972 study. Despite these differences, community diversity between the two periods followed a similar pattern. Therefore, while parameters indicate a worsening of conditions in Kingston Harbour, the pattern of distribution is very similar, suggesting that the areas experiencing the greatest stress remain the same.
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Document Type: Research Article
Publication date: 2003-09-01
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