Water Balance Characteristics Research Articles

Limnology of oligotrophic dune lakes at Cape Flattery, North Queensland

Physical, chemical and biotic attributes of 16 lakes and ponds in the siliceous dunefields of Cape Flattery, in the humid tropics of Australia, have been investigated. The dune lakes are similar to those of dunefields in south-eastern Queensland, with very low to low conductivity (62-338 �S cm-1), low pH (3.9-6.8), and low to high humic content (gilvin 0.0-31.0 g440 m-1). These lakes are apparently not perched above the local water table. The ionic compositions of all lakes were very similar, with NaCl predominating and with very low concentrations of Mg, Ca, K, and SO4. Bicarbonate was absent or negligible in most lakes. The oligotrophic lakes are characterized by a desmid-diatom limnetic plankton of moderate diversity (12-35 species per lake). Of 144 taxa of phytoplankton recognized, 58% were desmids and 15% diatoms. The zooplankton was of low diversity and dominated by Calamoecia ultima. Twenty-nine species of aquatic macrophytes and 11 species of fish were recorded. Freshwater turtles (possibly Chelodina rugosa Ogilby), and the estuarine crocodile, Crocodylus porosus Schneider, were recorded from some lakes. Principal component analysis of chemical data distinguished three groups of lakes: a series of humic-stained ponds and lakes, a group of clear-water lakes with little or no humic staining, and a former barrier lagoon. Cluster analysis of the phytoplankton flora consistently segregated the clear-water lakes from humic-stained lakes but, in general, concordance of chemical, physiographic and biotic characteristics was poor. Existing classification schemes for Australian dune lakes, based on similar sets of physiographic, chemical and biotic data, do not cater well for the Cape Flattery lakes. A more useful classification may derive from consideration of the hydrological processes influencing their water balance and chemical characteristics.

Relationships between water balance properties and habitat characteristics in the sibling Hawaiian Drosophilids, D. mimica and D. kambysellisi.

Four populations of Drosophila mimica and 1 population of D. kambysellisi collected at sites which differed in wetness were examined for several water balance characteristics. Net water loss per hour increased as av (relative humidity/100) decreased in all populations, but the rate of increase was lower in populations from dry sites. When exposed to 0.70 av, D. kambysellisi, which were from a rain forest, lost water faster and died sooner than did D. mimica. Two D. mimica collecting sites were divided into smaller units based on substrate type at one site and on litter wettness at the other site. The D. mimica at the first site were homogeneous with respect to the water balance properties studied here, but in the second site, there was evidence of population differentiation associated with litter wettness.

Comparison of Some Water Balance Characteristics in Several Drosophila Species Which Differ in Habitat

Although remaining in water balance is necessary for all organisms, the strategies for reducing water loss vary between species, depending on environmental conditions as well as on physiological and morphological considerations. Six species of Drosophila from 3 species groups and a variety of habitat types have been examined for some water balance properties. Two sibling species from Hawaii have been studied in more detail. All 6 species studied lose water rapidly at all test av's (relative humidity/100) below saturation, but the rates at which water loss increases when the av is lowered vary between species. The 2 Hawaiian species from different habitats are strikingly different in water balance properties and survival characteristics at 0.70 av. One population of D. mimica which was collected in a very dry area was much more tolerant of desiccation than were the other populations of the same species.

Studies on the relationship of water balance properties and survival in the Hawaiian drosophilid, D. Mimica

Some aspects of the relationship between water balance characteristics and biological fitness have been explored both for a laboratory-reared stock (K85P1) of Drosophila mimica and for each of four field-caught populations of D. mimica. At low a v 's, there is a clear correlation between water loss rates and survival time, but at saturation, the relationship is less striking. Neither body weight nor sex correlate strongly with water loss rate at 0.70 a v , but females survive longer than males. Some differences in the response to desiccation between populations from different collection sites are also suggested.

Physiological aspects of water balance in the Hawaiian drosophilid, Drosophila mimica

The ability to resist desiccation is an important component of biological fitness for terrestrial organisms. Several water balance characteristics have been studied for a strain of laboratory-reared Drosophila mimica and for four populations of D. mimica collected at sites differing in altitude and wetness. In the absence of drinking water, D. mimica are unable to maintain a water balance, even in nearly saturated environments. However, as a v ( a v = r.h. 100 ) decreases, transpiration does not increase as rapidly as expected and absorption remains nearly constant. The size of the fly is not correlated with its water loss characteristics, but some differences in regulation between the sexes are suggested.

The Water Relations of Some Desert Plants in Death Valley, California

The seasonal water relations of four plant species native to Death Valley were studied which were growing under both natural and irrigated conditions. These species included the winter annual, Camissonia claviformis , a summer-active herbaceous perennial, Tidestromia oblongifolia , and two evergreen perennials, Atriplex hymenelytra and, Larrea tridentata. Camissonia a plant with a high photosynthetic capacity had characteristics typical of most mesophytes under natural conditions and maintained high tissue water contents as well as high water and osmotic potential. Irrigation had little effect on these parameters for Camissonia. Tidestromia , which also has an unusually high photosynthetic capacity as well as a high rate of transpiration under natural conditions also has water balance characteristics not unlike many mesophytes although not to the same degree as Camissonia . The evergreen drought-enduring species which have a comparatively low photosynthetic capacity maintain low water and solute potentials at all seasons. Even at dawn when irrigated these species have low water potentials especially during the summer. In these xerophytes solute potential decreases during the course of the day. During the summer the plants under natural conditions have turgor pressures close to zero. The differential inherent photosynthetic capacities of these species are apparently strongly related to their inherent water balance characteristics.