Response of macroinvertebrates and small fish to nutrient enrichment in the northern Everglades

Abstract

Abstract:The northern Everglades (Water Conservation Area 2A) annually receives an excess addition of 60 M tons of phosphorus and 1814 M tons of nitrogen from agricultural run-off. During 1990--9 l, invertebrates were collected from replicate sweep and core samptes at eight sites along the nutrient enrichment gradient in Water Conservation Area 2A (WCA-2A). Species richness, Shannon's diversity, the number of unique species, and the density of invertebrates and small fish were all greater within enriched and intermediately enriched open water habitats than unenriched sloughs. Sorenson's taxonomic similarity index was significantly different between enriched and unenriched areas. Ostracods in particular were 14 times more abundant in the enriched area than at unenriched sites. The freshwater shrimp (Palaemonetes paludosus) was the only common species with lower densities in enriched than unenriched areas. However, the trophic structure or percent composition of grazers, predators, and collector-gatherers and the number &species within taxonomic orders and functional feeding groups was very similar among sites along the nutrient enrichment gradient. Higher invertebrate and small fish diversity and density within enriched sites indicates that nutrient enrichment has not caused direct harmful foodweb effects that may adversely influence higher trophic levels (e.g., wading birds). Assuming, however, that nutrients can cause cattails to overgrow and eliminate sloughs, the centers of biological diversity in the Everglades, then nutrient enrichment may have harmful indirect effects.

Macroinvertebrate and Fish Responses to Experimental P Additions in Everglades Sloughs

“…In addition to results reported by King (2001), results from Rader and Richardson (1994) support the notion that vegetation was an important factor governing the findings of the previous studies. Sampling with a sweep net and core sampler in patches of open water rather than dense stands of cattail along a 10-km P gradient in WCA-2A, they found the highest densities of macroinvertebrates at sites with the greatest enrichment of P. This trend mirrored the doseresponse curve of macroinvertebrate standing stocks to our experimental P gradient.…”

“…Nevertheless, this study highly suggests that local-scale P additions to oligotrophic Everglades sloughs will likely increase species richness of macroinvertebrates. Rader and Richardson (1994) also indicated that species richness increased with increasing levels of P enrichment based on observational data they collected in WCA-2A. They found that most taxa that were common to oligotrophic sloughs became more abundant in intermediately and highly enriched locations, while many new taxa were added to the community.…”

“…However, other authors have suggested that richness has declined due to P enrichment in the Everglades (Terczak 1980, Urban andKoebel 1992). Their work primarily was conducted in heavily-vegetated habitats rather than the open-water habitats sampled by Rader and Richardson (1994). Although not entirely conclusive, King (2001) indicated that taxon richness changed modestly along the P-gradient on a landscape scale, reaching greatest richness in the intermediately-enriched transition zone.…”

“…To date, only papers resulting from the P-dosing experiment that is presented in this chapter (King 2001, Qian, King, and Richardson 2003 have examined responses of invertebrates or fish to P enrichment using experimental manipulations. Moreover, relatively few observational studies have been conducted on Everglades invertebrates or fish in relation to nutrient enrichment (Terczak 1980, Urban and Koebel 1992, Rader and Richardson 1994, Jordan 1996, Turner et al 1999, King 2001, King and Richardson 2002.…”

Water Quality Parameters and Bird Diversity in Jagdishpur Reservoir, Nepal

“…When algae and plants are in abundance, higher trophic level organisms (e.g., invertebrates, fish, birds, mammals) that feed on these materials also often flourish (Weller 1981). Several small fish species (e.g., Gambusia) were two to three times more abundant in enriched portions of the everglades than in unenriched areas (Rader & Richardson 1994). For many lakes and reservoirs, eutrophication control is a major management objective.…”