Drought-related Changes Research Articles

Ichthyofauna of the sub-tropical Nhlabane Estuary, KwaZulu-Natal: drought-related changes in the fish community during extended mouth closure

The fish fauna of the Nhlabane estuary in northern KwaZulu-Natal was studied during a drought over the period 1992–95. The estuary mouth closed in late 1991, due to the drought as well as water abstraction from the system, and only reopened when the drought ended in late 1995. Fish were sampled by seine and gill-netting. Of 40 species recorded, most were estuarine-dependent marine species. Marine and estuarine dependent species dominated during 1992, whereas freshwater and resident estuarine species dominated in 1995. Estuarine-dependent marine species declined most in number and abundance and were most affected by the low salinities and lack of marine influence due to the lack of post-larval recruitment and the loss of the nursery function of the estuary. Exploitation of the Nhlabane system as a water resource also contributed to the extended mouth closure and the decline in the fish community. Limited post-larval recruitment by means of wave-overtopping did, however, appear to continue even though the estuary mouth remained closed.

Modelling the effect of drought on estuarine water quality

Long-term data assembled for monitoring the water quality of the Thames estuary between 1977–1992 were used to examine the changing influences of physico-chemical variables on estuarine water quality during drought conditions. Seasonal and monthly means were computed and tested for significant differences. Time series data were used to estimate regression models explaining observed variations in water quality parameter measurements during the predrought (1977–1988) and drought (1989–1992) periods. Stability tests were used to establish significant differences in predrought and drought models and to make inferences about the significance of drought induced low flows on water quality. Significant mean seasonal and monthly differences were found for flow, chlorinity, temperature, dissolved oxygen, pH and suspended solids. Total oxidisable nitrogen showed no significant change. Regression analyses were consistent with these results and highlighted the significance of drought related changes in flow and temperature for the determination of estuarine water quality. This suggests that management policies designed to mitigate the effects of drought be extended to consider their effects on estuarine water quality given the ecological importance of these areas.

Effects on invertebrate populations of drought-induced changes in estuarine water quality

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 203:133-143 (2000) - doi:10.3354/meps203133 Effects on invertebrate populations of drought-induced changes in estuarine water quality Martin J. Attrill1,*, Michael Power2 1Benthic Ecology Research Group, Plymouth Environmental Research Centre, University of Plymouth, Drake Circus, Plymouth PL4 8AA, United Kingdom 2Department of Biology, University of Waterloo, Waterloo, Ontario N2L 3G1, Canada *E-mail: mattrill@plymouth.ac.uk ABSTRACT: Between the years 1989 and 1992, severe drought conditions occurred in the Thames estuary catchment, significantly reducing freshwater flows into the estuary and affecting estuarine water quality. Long-term data assembled for water quality between 1977 and 1992 were combined with invertebrate abundance data obtained from the intake screens of West Thurrock power station over the same period. This allowed an examination of the influence of drought-induced changes in water-quality parameters on the populations of the most abundant mobile estuarine invertebrates. For 8 invertebrate species, seasonal and monthly means for pre-drought (1977 to 1988) and drought (1989 to 1992) abundances were calculated and tested for significant differences. Time-series data were used to estimate regression models explaining observed variations in populations of Carcinus maenas, Crangon crangon and Gammarus spp. during both periods. Stability tests were used to establish significant differences in pre-drought and drought models. Significant mean seasonal and monthly differences were found for C. maenas and Gammarus spp. in both winter and summer, with significant summer differences being apparent for C. crangon and Palaemon longirostris. Regression analyses confirmed these results for the modelled species and highlighted the significance of drought-related changes in temperature for all 3 crustaceans, with dissolved oxygen being an additional significant variable for C. crangon. The reported significant changes in abundance of the studied species during drought conditions have important implications for the structure and dynamics of estuarine food webs, as C. maenas, Gammarus spp., and particularly C. crangon, are either important predators on invertebrates and juvenile fish or major food items for estuarine fish species. KEY WORDS: Thames · Drought · Models · Carcinus maenas · Crangon crangon · Gammarus · Crustacea · Cnidaria · Ctenophora · Temperature · Oxygen Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 203. Online publication date: September 18, 2000 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2000 Inter-Research.

Nematodes From an English Chalk Grassland: Species Distributions

A total of 154 nematode species were identified from the chalk grasslands of Porton Down, a Site of Special Scientific Interest in southern England. Twelve soil samples were taken each January and June during 1990 and 1991 at two sites with differing vegetation and topographic position. The abundance of many species differed between the sites. There were also seasonal and probably drought-related changes in the abundance of many species. Some of the species distributions accord with previous records showing preferences by particular species for certain types of soil, others do not. Species are divided into generalist, intermediate and specialist species on the basis of spatial distribution. Seasonal, drought-tolerant, drought-susceptible and temporally stable species are recognized on the basis of temporal distribution. Patchy species are recognized on the basis of spatial land temporal distribution

Drought-related changes to geomorphologic processes in central Mali: Jacobberger, P A Bull Geol Soc AmV100, N3, March 1988, P351–361

Drought-related changes to geomorphologic processes in central Mali: Jacobberger, P A Bull Geol Soc AmV100, N3, March 1988, P351–361

Drought-related changes to geomorphologic processes in central Mali

Geomorphologic evidence exists for repetitive drought conditions in the African Sahel; within this framework of broad climatic changes through time, the 1968- 1985 drought episodes are not abnormal. The impact of recent drought on the economies and environments of Sahelian nations has been substantial, however, and the recovery capabilities off severely damaged lands are not well known. Study of the geomorphology and surface processes across a portion of Mali provides some constraints on the responses of desert fringe fluvial systems to changing environmental conditions. Multi-temporal orbital image data were used in combination with field investigation to map drought-affected soils, and to document changes to both fluvial and aeolian processes across the region of study. A combination of statistical methods yields consistent evidence of net albedo increases associated with particular landforms and surface processes over a nine-year interval. Although aeolian processes are a significant transport mechanism for removal and redistribution of soil materials, both orbital data and field study indicate that fluvial erosion is responsible for much of the primary topsoil loss and landform modification in this portion of the Sahel.