Comparative limnology of Sambhar and Didwana lakes (Rajasthan,NW India)

Two alkaline saline inland lakes of Indian arid region were studied during 1984 and 1985, to assess functioning and interaction of various environmental and biological factors. Changes in physical and chemical variables, planktonic composition, chlorophyll content and phytoplankton primary productivity were examined.Salinity in both lakes fluctuated from almost fresh water (1.80), to hypersaline (300) and acted as the main controlling factor for almost all the biotic parameters. Maximum total alkalinities were 2162 mg l^–1 and 2090 mg l^–1, respectively in Sambhar and Didwana lakes. Dissolved oxygen ranged from completely anoxic conditions to maxima of 11.68 and 7.29 mg 1^–1, respectively in Sambhar and Didwana lakes. Nutrient enrichment in the lakes was low.The phytoplankton species composition of Sambhar lake was reduced from an earlier reported 20 genera to only 11 (Nostoc, Microcystis, Spirulina, Aphanocapsa, Oscillatoria, Merismopedia, Nitzschia, Navicula, Synedra, Cosmarium and Closterium). Phytoplankton of Didwana was composed of only 9 genera including Anabaena and Nodularia. Sambhar lake, which once contained Artemia, is now totally devoid of them. On the other hand, Artemia was the most dominant zooplankter in Didwana lake at a salinity range of 15–288. Other zooplankters such as Moina, Cyclops and Brachionus flourished at lower salinity levels in Didwana lake. The seasonal quantitative and qualitative phyto- and zooplankton changes in relation to salinity are documented.     

Occurrence of parasitic watermolds in some lakes of Naini Tal,India

Five species of Olpidiopsis were noted in temperate and subtropical lakes of Naini Tal. Two species were new record for India.     

Population density of striped hyenas in relation to habitat in a semi-arid landscape,western India

We used camera trapping in conjunction with a spatial explicit capture–recapture model to estimate striped hyena (Hyaena hyaena) density and occupancy models to investigate factors affecting striped hyena detection probabilities in Ranthambhore Tiger Reserve (RTR), Rajasthan, India. A sampling effort of 4,450 trap days/nights over 75 days yield 68 photo captures of 21 unique striped hyenas (based on individual markings and visual identification); the estimated striped hyena density was 5.49?±?1.27 individuals/100 km². Results of our occupancy model suggested that a rugged terrain is an important factor that influences striped hyena detection probability. Correlation with striped hyena detection with human settlement provides evidence of social tolerance of striped hyena towards humans, and more occurrence of resources allowed coexistence of hyena in a human-dominated landscape. This elasticity (inhabited areas close to humans) demonstrated by striped hyenas is an exception among carnivore communities living in this semi-arid habitat.     

A comparison of phytoplankton assemblages in the Chesapeake and Delaware estuaries (USA), with emphasis on diatoms

The Delaware Bay is characterized as having greater nutrient and turbidity levels than the Chesapeake Bay. In reference to these differences, a one year study was conducted to identify any similarities and differences in the phytoplankton populations in these estuaries. The results indicated patterns of similarity in the diatom composition, with the total phytoplankton assemblage forming two site groups along a salinity gradient in each bay. These site groups were associated with stations located in the tidal fresh-oligohaline and meso-polyhaline regions of both estuaries. The seasonal concentrations of diatoms and total phytoplankton in both of these regions were higher in the Chesapeake Bay.Subtle differences between the two estuaries include a more diversified and abundant assemblage of neritic phytoplankters (including dinoflagellates) are present in the lower Chesapeake Bay. In contrast, a diatom dominated community is more characteristic of Delaware Bay. It is suggested the entry of neritic species into lower regions of the estuaries was enhanced by the reduced amount of rainfall and flow rates that occurred during the study period. The greater success of neritic species in the Chesapeake Bay is attributed to the lower turbidity of that estuary compared to Delaware Bay.     

Seasonal Abundance and Occurrence of the Asian Isopod Synidotea laevidorsalis in Delaware Bay, USA

In 1999 the marine isopod Synidotea laevidorsalis (Miers 1881), indigenous to the northwest Pacific, was first documented in Delaware Bay, USA. We monitored weekly recruitment of this isopod and several other motile species in the Maurice River, a tributary of Delaware Bay. A spatial survey was also conducted. Abundance of S. laevidorsalis varied seasonally but overwhelmingly dominated other co-occurring species by an order of magnitude or more throughout most of the year. Isopod abundance increased through the summer of 2004 and peaked in September, coincident with the passing of Hurricane Ivan. Field observations documented large populations, frequently associated with pilings and buoy lines, throughout Delaware Bay in salinities of 4 through 22 ppt. The dramatic abundance of this isopod indicates that there is considerable potential for altering community structure. This isopod has yet to be observed along the Atlantic Coast of New Jersey or in Chesapeake Bay, but it has been reported near Charleston, SC.     

Long-term changes in chemical features of waters of seven Ethiopian rift-valley lakes

Chemical and chlorophyll a concentrations of seven Ethiopian rift-valley lakes were studied during 1990–2000. Results were compared with studies made between 1960 and 1990 in an attempt to detect long-term changes. Three different trends are apparent in the salinities (and the correlates conductivity, alkalinity, sodium concentration) of these lakes over the last 40 years: three lakes (lakes Zwai, Shalla and Abaya) have maintained their salinity levels from the 1960s, two lakes (lakes Langano and Awassa) have become more dilute, and the salinity levels of Lake Chamo and the soda lake Abijata have increased. Concentrations of silicate decreased in almost all the lakes whereas soluble reactive phosphorus (SRP) increased in most lakes. Chlorophyll a concentrations were higher in the recent samples from all lakes except two, which in conjunction with results from SRP and silicate analyses suggest eutrophication in four out of the seven lakes studied. The study relates salinization in lakes with closed drainage to increased human activities in their catchments, intensified by changes in climate during the last three decades in sub-Saharan Africa.     

Occurrence of water molds in relation to hydrogen ion concentration in some lakes of Nainital,India

26 species of water molds belonging to Blastocladiales, Saprolegniales, Lagenidiales and Peronosporales were found to be different in their pH tolerance.     

Shoreline processes and establishment of Phragmites australis in a coastal plain estuary

Phragmites australis occurs extensively along undisturbed salt-marsh shorelines of Delaware Bay. The species has been considered indicative of human disturbance when found in estuarine marshes in the USA. It is suggested that geomorphic processes associated with coastal submergence provide an analog of human disturbances which can enable Phragmites australis to become established naturally. Deposition of sand bodies (or rafted debris) can suppress existing vegetation and allow Phragmites to become established. Subsequently, even if the sand or debris is moved, erosional truncation of the intertidal profile can inhibit recolonization by the original dominant shoreline species, Spartina alterniflora.     

Large-scale climatic signatures in lakes across Europe: a meta-analysis

Recent studies have highlighted the impact of the winter North Atlantic Oscillation (NAO) on water temperature, ice conditions, and spring plankton phenology in specific lakes and regions in Europe. Here, we use meta-analysis techniques to test whether 18 lakes in northern, western, and central Europe respond coherently to winter climate forcing, and to assess the persistence of the winter climate signal in physical, chemical, and biological variables during the year. A meta-analysis approach was chosen because we wished to emphasize the overall coherence pattern rather than individual lake responses. A particular strength of our approach is that time-series from each of the 18 lakes were subjected to the same robust statistical analysis covering the same 23-year period. Although the strongest overall coherence in response to the winter NAO was exhibited by lake water temperatures, a strong, coherent response was also exhibited by concentrations of soluble reactive phosphorus and soluble reactive silicate, most likely as a result of the coherent response exhibited by the spring phytoplankton bloom. Lake nitrate concentrations showed significant coherence in winter. With the exception of the cyanobacterial biomass in summer, phytoplankton biomass in all seasons was unrelated to the winter NAO. A strong coherence in the abundance of daphnids during spring can most likely be attributed to coherence in daphnid phenology. A strong coherence in the summer abundance of the cyclopoid copepods may have been related to a coherent change in their emergence from resting stages. We discuss the complex nature of the potential mechanisms that drive the observed changes.     

Cocos sahnii Kaul: A Cocos nucifera L.-like fruit from the Early Eocene rainforest of Rajasthan, western India

Cocos sahnii Kaul, a fossil palm fruit, is validated and described from the Fuller's earth deposits of Kapurdi village of Rajasthan considered as Early Eocene in age. The fossil best resembles the genus Cocos, particularly Cocos nucifera L., which is now a common coastal element thriving in highly moist conditions. The recovery of this coconut-like fruit, along with earlier described evergreen taxa from the same formation, suggests the existence of typical tropical, warm and humid coastal conditions during the depositional period. The present arid to semi-arid climatic conditions occurring in Rajasthan indicate drastic climate change in the region during the Cenozoic. The possible time for the onset of aridity in the region which caused the total eradication of semi-evergreen to evergreen forests is discussed, as well as the palaeobiogeography of coconuts.     

Diurnal variation in physical-chemical properties and primary production in the interconnected marine,mangrove and freshwater biotopes of Kakinada coast,Andhra Pradesh,India

Diurnal variation in hydrological variables and dissolved inorganic nutrients such as PO _inf4 ^sup3– -P, N O _inf2 ^sup– -N, NO _inf3 ^sup– -N and NH _inf4 ^sup+ -N were studied in three interconnected biotopes including freshwater, marine and mangrove brackish water of the Kakinada coastal zone, Andhra Pradesh. Samples were collected at intervals of 3 hours, for a period of 24 hours. In the marine environment salinity varied from 26 to 32 whereas in the mangrove waters it fluctuated from 12 to 20 and in both biotopes salinity showed bimodal type of oscillation. Dissolved oxygen content was high in the mangrove waters during day time but decreased rapidly during the night hours. In the marine environment PO_f4 ^p3–-P concentration varied from 0.345 to 1.195 g at l^–1, NO _inf3 ^sup– -N from 1.03 to 6.62 g at l^–1 and NO _inf2 ^sup– -N from 0.086 to 0.506 g at l^–1. The highest and the lowest concentrations of PO _inf4 ^sup3– -P, NO _inf3 ^sup– -N, NO _inf2 ^sup– -N recorded in the mangrove waters were 0.790 and 0.325 g at l^–1, 7.10 and 1.60 g at l^–1 and 0.278 and 0.060 g at l^–1, respectively. The concentration of PO _inf4 ^sup3– -P, NO _inf3 ^sup– -N and NO _inf2 ^sup– -N were high in the freshwater canal, the maximum and minimum values being 1.110 and 0.730 g at l^–1, 26.40 and 9.98 g at l^–1 and 0.520 and 0.252 g at l^–1 respectively. The concentration of ammonia was relatively high in the mangrove water. Gross and net primary production in the mangrove water was 4 times higher than in the marine biotope. There was no export of dissolved nutrients from the mangrove environment to the adjacent marine waters.     

Effects of zooplankton on sedimentation in pelagic ecosystems: Theory and test in two lakes of the Canadian shield

A simple heuristic theory based on conservation of matter and describing the fate of autotrophic production in pelagic ecosystems was developed to assist in conceptualizing how zooplankton affect sedimentation processes in lakes and oceans. The theory predicted that effects of zooplankton on the fraction of autotrophic incorporation that sediments (the export ratio) will be a function of factors related both to zooplankton digestion and egestion and to tendencies of particulate matter to sediment directly prior to mineralization. As a result, effects of zooplankton grazing on the export ratio were predicted to be site-dependent, a function of physical conditions and zooplankton communities characterizing an ecosystem. The theory was tested by monitoring autotrophic production of C, N, and P, sedimentation of C, N, and P, and zooplankton biomass in two lakes of the Canadian shield characterized by contrasting morphometry and food-web structure. In Lake 110, a small elongate lake protected from wind exposure, export ratios of C, N, and P declined strongly with zooplankton biomass. In contrast, in L240, a larger lake with considerably greater wind exposure, export ratios increased with zooplankton biomass. These results were consistent with predictions of our theory that effects of zooplankton on sedimentation processes will depend on the tendency of particulate matter to directly sediment relative to the tendency of egested materials to sediment. However, no significant differences in relationships between export ratios for C, N, and P and zooplankton biomass were found.     

Physical and chemical limnology of 204 lakes from the Canadian Arctic Archipelago

The physical and chemical limnology of 204 lakes from across the Canadian Arctic Archipelago was examined. Mean summer air temperature did not correlate well with lake chlorophyll levels due to the predominance of ultra-oligotrophic hard-water lakes located in a polar climate. Local geology influences ion budgets and is an important factor in determining pelagic phosphorus availability, carbon cycling and metal concentrations. Ratios of particulate carbon, particulate nitrogen and chlorophyll a indicate that planktonic microorganisms are not always the major producers of organic carbon in arctic lakes. Allochthonous particulate matter contributes significantly to the carbon and phosphorus budgets of small and mid-sized lakes across the Arctic, although the availability of these elements is controlled by many interacting geochemical and biological factors. Phosphorus is generally limiting, however, increases in available phosphorus, nitrogen and carbon are all required to make significant long-term differences in lake productivity. Particulate phosphorus levels can be high in lakes where phosphorus-rich shales or carbonatite bedrock are present. These phosphorus-enriched lakes are found in several areas across the mid-arctic islands, however, only small amounts of this nutrient are available as soluble reactive phosphorus. Although lakes throughout the Arctic are typically ultra-oligotrophic, they still represent an important sink for allochthonous nutrient deposition.     

Seasonal variation in the water quality and chlorophyll a of semi-intensive shrimp ponds in a subtropical environment

Twelve water quality variables were measured at different intervals (biweekly and twice a week) in two ponds during two consecutive production cycles in a semi-intensive shrimp farm on the Northwest coast of Mexico. The average harvest during dry season (March–July, a 95 days period) was 1822 kg ha^-1, with an average size of 16.0 g; while the harvest in the rainy season (August–January, a 165-day period) was 2125 kg ha^-1, with an average size of 11.9 g. In the rainy season, dissolved oxygen concentration tended to decrease as the feeding rates and shrimp and phytoplankton biomass were increasing until harvest. During both culture cycles, mean values of temperature, salinity and ammonium in ponds were not significantly different from those in inlet water, whereas pH levels in ponds were higher than in incoming water.Nitrogen nutrients, pH and particulate organic matter levels in ponds and inlet water did not exhibit seasonal differences; the better yield and feed conversion obtained during rainy season reflect the fact that temperature and mean chlorophyll a were higher during the rainy than in the dry season; salinity and total suspended solids were lower during the dry than in the rainy season. The mean levels of the water quality variables in the two ponds were not significantly different in both grow out cycles. Therefore, the differences in productivity between ponds cannot be explained by the water quality.     

Late fall phytoplankton dynamics in three lakes, Rocky Mountain National Park

We studied phytoplankton population dynamics during the month preceding formation of ice cover in three small subalpine lakes in Rocky Mountain National Park, Colorado, U.S.A. The outflow from Emerald Lake, which is surrounded by talus, flows into Dream Lake, which is surrounded by sub-alpine forest. Nymph Lake is a lower seepage lake with abundant macrophytes in summer. The major ion concentrations in the three lakes were similar during the study, although Emerald and Dream Lakes had higher concentrations of nitrate and silica than Nymph Lake. A principal component analysis (PCA) showed that the phytoplankton in Emerald and Dream Lakes were distinct from the phytoplankton in Nymph Lake. The species composition changed in each lake during the late fall. The patterns of change in Emerald and Dream Lakes were similar on the PCA diagram despite the greater abundance of diatoms in Dream Lake and the decreasing flow from Emerald Lake into Dream Lake during the fall. In Nymph Lake, a progressive shift in species distribution occurred with a decrease in the most abundant chlorophyte, Chlamydomonas sp., and increases in several species, including two chrysophytes and the diatom Eunotia sp. The marked change in species composition in all three lakes suggests that phytoplankton populations are influenced by changes in water temperatures and incident solar radiation that occur during the late fall. We also compared these data with phytoplankton data for two fall periods from two other hydrologically connected Rocky Mountain lakes. PCA analysis showed that the difference between years was greater than the change during the fall and that the fall species composition in these two lakes was distinct from that in Emerald and Dream Lakes or in Nymph Lake. Studying phytoplankton dynamics in alpine and sub-alpine lakes may offer clues as to how these ecosystems may respond to projected climate changes in the Rocky Mountain region, such as warmer temperatures and later formation of ice-cover.     

Water quality research in Loosdrecht lakes: the salient features

Ecosystem research by the working group Water Quality Research Loosdrecht lakes (WQL) was carried out from 1979 to 1990. A coordinated research programme, involving several research institutes and laboratories in The Netherlands, was initiated in 1983, i.e. a year before the reduction of external phosphorus loading by stripping, became effective. The paper summarizes the main results, with emphasis on insight they provide into the lake ecosystems.     

Estimation of Primary Productivity by Chlorophyll a in vivo Fluorescence in Freshwater Phytoplankton

Primary productivity in marine waters is widely estimated by the measurements of ¹⁴C incorporation, the underwater light climate, and the absorption spectra of phytoplankton. In bio-optical models the quantum efficiency of carbon fixation derived from ¹⁴C incorporation rates, the photosynthetically absorbed radiation derived from the underwater light climate, and the phytoplankton absorption spectra are used to calculate time- and depth-integrated primary productivity. Due to the increased sensitivity of commercially available fluorometers, chlorophyll a in vivo fluorescence became a new tool to assess the photosynthetic activity of phytoplankton. Since fluorescence data yield only relative photosynthetic electron transport rates, a direct conversion into absolute carbon fixation rates is not possible. Here, we report a procedure how this problem can be adressed in freshwater phytoplankton. We adapted a marine bio-optical model to the freshwater situation and tested if this model yields realistic results when applied to a hypertrophic freshwater reservoir. Comparison of primary productivity derived from ¹⁴C incorporation to primary productivity derived from Chl a fluorescence showed that the conversion of fluorescence data into carbon fixation rates is still an unsolved problem. Absolute electron transport rates calculated from fluorescence data tend to overestimate primary production. We propose that the observed differences are caused mainly by neglecting the package effect of pigments in phytoplankton cells and by non-carbon related electron flow (e.g., nitrogen fixation). On the other hand, the ¹⁴C incorporation rates can be artificially influenced by "bottle effects", especially near the water surface, where photoinhibition, photorespiration, and Mehler reaction can play a major role.