Joseph Prenger

Benthic macroinvertebrates of small Florida pondcypress swamps and the influence of dry periods

Benthic macroinvertebrate communities were sampled bimonthly from December 1993 to April 1995 in three small pondcypress swamps. Eighty-five taxa were collected, with Chironomidae, Dytiscidae, and Hydrophilidae contributing large numbers of genera. Annual mean density was 4,229 individuals/m2, and monthly densities for individual ponds ranged from 950 to 11,623 individuals/m2. Three genera,Crangonyx (Amphipoda),Polypedilum, andChironomus (Chironomidae), accounted for 70% of the total density. High levels of temporal and inter-pond variability were documented. Taxon richness and total density of communities sampled during drawdown were similar to those of wet months. The large number of taxa unique to the dry period contributed substantially to overall taxon richness. The benthic macroinvertebrate communities of these systems seem to be adapted to unpredictable drawdown.

Predictors of seasonal oxygen levels in a Ugandan swamp/river system: a 3-year profile

Oxygen scarcity is widespread in tropical fresh waters, particularly in floodplain pools, inundated forests, dry season pools in intermittent streams, and permanent swamps (CARTER 1955, I<RAMER et al. 1978, WELCOMME 1979, }UNK et al. 1983, CHAPMAN & I<RAMER 1991). In East Mrica, hypoxia is prevalent in extensive dense wetlands dominated by papyrus (Cyperus papyrus) (CARTER 1955, BEADLE 1981, CHAPMAN et al. 1998). In dense papyrus stands, which average 3-4 m in height and can reach up to l O m (THOMPSON et al. 1979), the terminal brushlike umbels form a closed canopy leaving the interior of the stand dark and cool. Such swamps are poorly mixed, have minimal incident light and high rates of organic decomposition of water logged vegetation leading to extremely hypoxic waters (CARTER 1955, THOMPSON 1976, CHAPMAN & LIEM 1995, CHAPMAN et al. 1998). Increased water flow associated with seasonal rains elevates dissolved oxygen levels in these dense swamps producing a strong cycle of oxygen availabi!ity (HOWARD-WILLIAMS & GAUDET 1985, CHAPMAN et al. 1998). However, lateral expansion and flushing of reducing organic matter from papyrus swamps with the onset of such rains may cause pronounced temporallags in seasonal increases in oxygen behind those exhibited by stream and river sites with limited floodplain inundation.

Cultural eutrophication of a Ugandan highland crater lake: a 25-year comparison of limnological parameters

Volcanic crater lakes are widely disrributed throughout the tropics. Although early limnological expeditions to East Africa focused on large spectacular lakes, the SUNDA expedition of 1928-29 paid particular attention to crater lakes throughout Indonesia (RUTINER 1931, CRISMAN & STREEVER 1996). A modest resurvey of the Indonesian crater lakes has been conducted (GREEN et al. 1996). In spite of early surveys (JuDAY 1915, DEEVEY 1957), interest in Central American crater lakes has lagged umil recently (BARLOW et al. 1976, }IMENEZ & SPRINGER 1994, UMANA &J!MENEZ 1995). Our understanding of crater lakes in Ghana (WHYTE 1975) and Cameroon (.Kl.ING 1988) in West Africa and Ethiopia (Wooo er al. 1984, GREEN 1986, ZrNABU 1994) and Kenya (MELACK 1996) in East Africa is slowly developing. The earliest investigations on crater lakes in Uganda were by BEADLE (1932, 1963, 1966). La t er, MELACK (1978) surveyed the fo ur geographic dusters of crater lakes in western Uganda and divided rhe 89 lakes into broad groups, saline lakes (conductiviry > 15,000 flmhos/cm) and dilute lakes (conductivity <l ,000 flmhos/cm). Recent investigations on dilute crater lakes of the western Ugandan Highlands near Fort Porta! have been focused o n physicall chemical parameters (KrZITO et al. 1993, CHAPMAN er al. 1998, LrviNGSTONE unpublished) and plankton (Krzrro & NAUWERCK 1995). Dilute crater lakes serve as an important water supply for h uman populations in rural areas o f western Uganda. With a 3.4%/annum growth rate in the human population and an associated deforestation rate of 1.3%/annum, the qualiry of this essential water supply is in danger (KAUFMAN et al. 1996). Forests are currently being deared even o n the steepest crater walls for agriculture and firewood. The purpose o f the current paper is to presem the initial results from a limnologicallpaleolimnological investigation of o ne of the few eutrophic crater lakes in western Uganda. We present a 3-year database for dissolved oxygen and temperarure for multiple sites within the basin and compare these with hisrorical data collected by MELACK in 1971. Possible landscape modifications are discussed as causal mechanisms for the observed eutrophication.

Correlation of vegetation and benthic macroinvertebrate community changes in Florida pondcypress swamps following clearcutting

Forested wetlands dominated by pondcypress (Taxodium distichum var. nutans (Ait) Sweet) were onee thought of as uninhabitable areas suitable only for logging or draining. Pond cypress swamps (also known as eypress domes and cypress ponds) are now known to be important eeonomieally and environmenrally as nutrient sinks, hydrologieal buffers, and wildlife habitats (MITSCH & GossELINK 1993). lnereased emphasis on the preservation of forested wetlands has resulred in studies addressing rhe effeets of anthropogenie disturbanees sueh as flooding (LuGo & BROWN 1984), drawdown (LESLIE et al. 1997), logging (e.g. NEWBOLD et al. 1980, AusT et al. 1995, LESLIE 1996), fire and nutrienr loading (EWEL 1984) on these habitats. Understanding the eeologieal sueeession of natural systems following disturbanee is key to determining how best to manage rhe systems to mainrain eeosystem strueture and funetion (LuGo 1984).