5.2.2. Karst Freshwater Systems
Karst Freshwater Systems represents both the subterranean aquifer and above-ground springs and rivers. Rainfall in the Cockpit Country recharge area percolates quickly through the thin vegetative humus and topsoil and enters cracks and crevices in the limestone bedrock to find its way into the cave aquifer system. The water percolating through the soil layers increases in acidity, primarily from the exposure to carbon dioxide. Carbonic acid in the groundwater dissolves the limestone bedrock, enlarging the fractures into conduits. Percolation also delivers clay sediments and dissolved and particulate organic matter that constitute the food base for aquatic organisms. These aquatic organisms also are dependent on a range of water chemistry variables (water quality) and the occurrence of these species in groundwater systems is an indicator of good water quality. In low-lying areas of the cockpit karst, ephemeral and permanent pools (" blue holes" ) and springs emerge to form the headwaters of river systems that drain in coastal marine areas. The two major above-ground water systems are the Martha Brae, the source of which emerges in Windsor, Trelawny, and the Black River, which receives major inputs from a set of deep pools located near Aberdeen in southern Cockpit Country. The riverbanks of all above-ground river systems emanating from Cockpit Country are degraded, with little native vegetation remaining.

Two ecological processes that are important for maintaining Karst Freshwater Systems are (1) hydrologic regimes and (2) organic matter flux (see also Table 1). Like most headwater streams, subterranean streams are heterotrophic systems that rely almost entirely upon outside sources of energy. Organic matter that is present is usually of low food quality, and as such, most cave systems are severely nutrient limited (oligotrophic). The majority of energy input is in the form of dissolved organic matter (DOM) transported in the cave stream, except for cave systems with significant fecal inputs (bat guano, insect frass). Floods import most of the organic matter in cave streams, and in some caves, flood/drought cycles regulate the life cycles of cave biota. The microbial community transforms this DOM into biomass that is consumed by higher trophic levels. Subterranean food webs are fundamentally detrital, relying upon microbes and invertebrates to assimilate and enhance the few organics present.

Nutrient pollutants alter the oligotrophic nature of ground-water ecosystems and severely alter ground-water food webs. The introduction of organic pollution can extirpate the indigenous fauna or completely replace the community with fauna from the surface. Enrichment in cave systems could favor surface-dwelling species, which are physically stronger, more active, and have higher fecundities than subsurface-dwelling species. Such enrichment could increase the food supply and thus the payoff for epigean species, which may invade such disturbed caves and increase the risk of competition with or predation of cave fauna. In general, moderate pollution by sewage-derived organic matter results in a loss of biodiversity (especially intolerant species) and an increase in the standing crop of tolerant species.

The experts judged the overall biodiversity health of Karst Freshwater Systems to be " GOOD" (Table 2). Size was considered " GOOD" based on reported lowering of the groundwater table associated with over-pumping (i.e., overall volume has decreased). Data are lacking for the condition of freshwater systems throughout the aquifer but experts were sufficiently concerned about nutrification associated with sub-standard septic systems in peripheral communities and the concomitant contamination of above-ground river systems to judge the condition of Karst Freshwater Systems as " FAIR."

Other stresses affecting freshwater systems are associated with disruptions to the essential processes that maintain the quality of freshwater habitats: hydrologic regime, sedimentation regime, water chemistry, nutrient concentration, altered species composition, and altered food web regimes (Table 5). These changes are the result of an altered ecological context in the karst landscape surrounding the well-developed cockpit karst: almost complete loss of riverine forest, extensive loss of watershed forest cover, and conversion to agriculture, with associated incompatible practices (Table 6). As with the Wet Limestone Forest target, should mining and quarrying occur, the effects to the ecological integrity of Karst Freshwater Systems will be irreversible.