Annual and Seasonal Rainfall Trends in an Equatorial Tropical River Basin in Malaysian Borneo

Annual and seasonal rainfall trends in the Limbang River Basin (LRB), located in the equatorial tropics of Malaysian Borneo, have been characterised through Mann-Kendall and Spearman’s Rho non-parametric tests. Rainfall from 13 rain gauge stations in the LRB for the period 1948–2016 was examined in the present study. Basic statistical analysis of rainfall in the region indicates normal distribution, low missing percentage and homogenous characteristics of precipitation. Annual and seasonal rainfall in the LRB shows spatial variation while considering different rain gauge stations. In annual rainfall, eight stations showed a decreasing trend and five stations showed an increasing trend. Rain gauge stations which showed a statistically significant increase in annual rainfall were Limbang DID (2.77 and 2.85 mm/year) and Long Napir (3.65 and 3.77 mm/year). In recognising the two annual monsoon seasons in this area, a significant increase in rainfall was noticed in Long Napir (2.79 and 2.88 mm/year) during the Southwest monsoon (SWM) period. During the Northeast monsoon (NEM), along with Long Napir (3.90 and 3.95 mm/year), Limbang DID (2.86 and 3.02 mm/year), Pandaruan (1.82 and 1.87 mm/year) and Medamit Nanga (1.93 and 2.00 mm/year) also showed a significant increase in rainfall. At the same time, a distinct trend was noticed in rainfall amounts during the inter-monsoon (IM) periods. During the first inter-monsoon month (April), seven rain gauge stations showed an increasing trend in rainfall, whereas in the second inter-monsoon month (October), nine stations showed a decreasing rainfall trend. In April, Long Napir (1.86 and 1.95 mm/year) indicated a significant increasing trend, whereas in the month of October, the rain gauge station at Ukong showed a significant decreasing trend (− 2.45 and − 2.37 mm/year). Though minor spatial changes in trend characteristics were observed among the rain gauge stations, the LRB as a whole showed a consistent increasing (significant and non-significant) trend in annual and seasonal rainfall.

     

Assessment on Seasonal Variation of Groundwater Quality of Phreatic Aquifers – a River Basin System

Spatial distribution of pH, electrical conductivity (EC), total dissolved solids (TDS), fluoride and total iron content of ground water samples collected from the muvattupuzha river basin, Kerala, India, has been studied for pre monsoon and post monsoon periods of year 2001. Results showed the groundwater of the basin is acidic for which the pH values ranged between 5.5 and 8.0. Average EC was found to be less than 100 μS/cm, for most of the study region. The pre monsoon minimum and maximum TDS were found as 25.6 and 227.84 mg/L respectively, where as post monsoon values ranged between 16 and 162.56 mg/L. The relatively low EC and TDS values found both during the seasons in the lateritic terrain of the river basin signifies the lower residence time of ground water with the country rock. This makes the groundwater quality of this river basin as good. Pre monsoon season samples showed high total iron content than that during the post monsoon period. During the study period values of the fluoride contents were found to be within the permissible limits.     

Historical pollution trends in coastal environments of India

Seventeen sediment cores were collected from different coastalecosystems of Tamil Nadu, India that include coastal lagoon (Pulicat), polluted rivers in Chennai (Adyar and Cooum), Coral reef (Gulf of Mannar) and a perennial river (Tamiraparani).Radiometric dating has been used to determine the modern sedimentation rates in these ecosystems. The Pulicat Lake and thepolluted rivers (Adyar and Cooum) yield an average sediment accumulation rate of 12.34 and 7.85 mm yr^-1, respectively. Inthe Gulf of Mannar coral reef, the sedimentation rate averages 17.37 mm yr^-1, while the rate in Tamiraparani River is 11.00 mm yr^-1. In the Tamiraparani River basin, the deposition rates were an order of magnitude higher when compared to the erosion rates, which may be due to bank erosion and the intense human activity. In general high rates of sedimentation observed in the coastal ecosystems not only reflect the capacity of the coastal regions as sinks for trace metals but also denoteincreased input of pollutants into the coastal environments in the recent past. The deposition rates of heavy metals – Fe, Mn,Zn, Cu, Cr and Ni in the depth profiles have been computed using sedimentation rates and their distribution is discussed. It can be seen that the mean deposition rates of all the measured elements in the Tamil Nadu coastal ecosystems are high compared with rates determined for the sediments of the deltaic regions ofIndia and the Bay of Bengal.     

Freshwater aquatic macrophytes as heavy metal monitors — the Ottawa River experience

The ability of freshwater aquatic vascular plants to accumulate heavy metals was examined in some detail during a five year study. Differences in uptake rate were found to depend on the species of plant, the seasonal growth rate changes and the metal ion being absorbed. Lead and mercury were concentrated to a greater extent than the lighter nickel and copper. Laboratory experiments were designed to establish uptake rate constants which were used to calculate water concentrations of mercury from the analyses of plant samples from the river. Background levels of mercury in aquatic plants of 35–50 ng g^-1 dry weight corresponded to a water concentration near 15 ng L^-1 of total mercury of which 25–30% was methylmercury. Higher concentrations of mercury in the plants indicated a proportional increase in the mercury level in the water.     

Spatial and seasonal characteristics of river water chemistry in the Taizi River in Northeast China

Anthropogenic activities have led to water quality deterioration in many parts of the world, especially in Northeast China. The current work investigated the spatiotemporal variations of water quality in the Taizi River by multivariate statistical analysis of data from the 67 sampling sites in the mainstream and major tributaries of the river during dry and rainy seasons. One-way analysis of variance indicated that the 20 measured variables (except pH, 5-day biological oxygen demand, permanganate index, and chloride, orthophosphate, and total phosphorus concentrations) showed significant seasonal (p?≤?0.05) and spatial (p?<?0.05) variations among the mainstream and major tributaries of the river. Hierarchical cluster analysis of data from the different seasons classified the mainstream and tributaries of the river into three clusters, namely, less, moderately, and highly polluted clusters. Factor analysis extracted five factors from data in the different seasons, which accounted for the high percentage of the total variance and reflected the integrated characteristics of water chemistry, organic pollution, phosphorous pollution, denitrification effect, and nitrogen pollution. The results indicate that river pollution in Northeast China was mainly from natural and/or anthropogenic sources, e.g., rainfall, domestic wastewater, agricultural runoff, and industrial discharge.     

SEASONAL INFLUENCES OF THE ORGANIC POLLUTION MONITORING OF THE NEW CALABAR RIVER, NIGERIA

Monitoring of the New Calabar River water was conductedmonthly for a period of one year to ascertain seasonalinfluences and industrial effluent discharges on the organicpollution status of the river. Dissolved oxygen (DO) levelsranged between 3.4 and 9.1 mg/l and 4.4–9.0 mg/l for therainy and dry seasons respectively. Total dissolved solids(TDS) levels ranged between 6.5 and 4013.9 mg/l for the rainyseason and 4.32–619.5 mg/l for the dry season. The ranges forthe organic pollutant parameters were: biochemical oxygendemand, 0.25–4.20 mg/l and 0.15–4.95 mg/l; COD, 10–1000mg/l and 15–100 mg/l; oil and grease, 0.00001–5000 g/l and0.00001–800 g/l; anionic surfactants, 2.0–30 gMBAS/l and 0.1–2.0 g MBAS/l for the rainy and dryseasons respectively. The ranges for the same parameters forthe industrial effluent were: DO, 2.1–3.9 mg/l and 6.5–10.8mg/l; BCD, 0.35–1.4 mg/l and 2.3–2.7 mg/l; COD, 508 mg/l and20–576 mg/l; oil and grase, 0.07–50 g/l and0.048–25.0 g/l; and anionic surfactants, 4.0–7.3g MBAS/l and 0,2–17.0 g MBAS/l for the rainyand dry seasons respectively. These results indicate thatseasonal changes as well as industrial effluent dischargesinfluenced the organic load of the river.     

Changes in Soil Properties of Abandoned Shrimp Ponds in Southern Thailand

Chemical soil properties between active shrimp ponds andabandoned ones on the Bangkok soil series were compared,at Ranote District, Songkhla Province in southern Thailand.Soil samples were collected at depth intervals of 0–10, 10–20, 20–30, 30–40 and 40–50 cm from pond bottoms at the same ponds used in a former study conducted in 1994, fora total of 6 ponds with 3 sampling sites for each pond. Theseponds were active during the previous study in 1994, abandonedin 1996 and investigated by this study in 1999. All the samples were analyzed for exchangeable Ca, Mg, K and Na electrical conductivity (EC), organic matter, S, P and pH, and statistically compared with the analytical results of theprevious study. An increase in amounts of Ca, Mg, K, Na and EC in the abandoned ponds as compared with the active ones by1.3–3.4, 1.4–2.1, 7.0–30.0, 1.2–6.3 and 1.3–10.9 timesrespectively was observed. That more of these elements weregained than lost each time the seawater was introduced intothe ponds, is explained by the Element Input/Output Consideration as proposed herein. Furthermore, a decreasein organic matter, S and P was also observed in the abandonedpond soils, and attributed to the absence of shrimp food and shrimp excreta following the cessation of shrimp raising activities. An unexpected decline in the soil pH of the abandoned ponds was found as well. Aerobic decomposition of organic matter during the absence of shrimp raising activitiescaused by soil microorganisms triggering SO₂ and H₂SO₄ formation probably played a more significantrole than the increase in the amounts of the basic elements (Ca, Mg, K, and Na) eventually reducing soil pH in the abandoned ponds. The significant depletion of the amounts of organic matter in the abandoned pond soils also supports this observation.     

Spatio-temporal variation in the hydrochemistry of Tawa River, Central India: effect of natural and anthropogenic factors

Tawa River is the biggest left bank tributary of the Narmada, the largest west-flowing river of the Indian peninsula. Central India enjoys a tropical climate, is highly urbanized, and the river flow is mostly controlled by monsoon; a large part of the population depend on rivers for their livelihood. Spatial and temporal variations in the hydrochemistry of the Tawa River were studied based on seasonal sampling along the course of the river and its tributaries. The study is important because not much data exist on small size rivers and the river processes spell out correctly in smaller basins. The monsoon season accounts for more than 70 % of river water flow. The basin is characterized by silicate lithology; however, water chemistry is controlled by carbonate-rich soils and other weathering products of the silicate rocks, as indicated by the high (Ca?+?Mg)/(Na?+?K) ratios (>3.8). The values of the Na-normalized ratios of Ca²⁺, Mg²⁺, and HCO₃ ^? suggest that both the carbonate and silicate lithology contribute to the hydrochemistry. On average, 42 % of HCO₃ ^? in the Tawa River water is contributed by silicate weathering and 58 % from carbonate lithology. The water remains undersaturated with respect to calcite during the monsoon and post-monsoon seasons and supersaturated during the pre-monsoon season. A significant influence of mining in the basin and other industrial units is observed in water chemical composition.     

Assessment of temporal variation in water quality of some important rivers in middle Gangetic plains, India

The study explains water quality of three important tributaries of the Ganga River in the middle Gangetic plains in India. Seasonal changes in the water quality of the studied rivers: Gandak, Ghaghra, and Sone were observed. During monsoon, several water quality parameters show considerable changes due to increased runoff from the catchments and other seasonal factors. Multivariate discriminant analysis delineated a few parameters responsible for temporal variation in water quality. Seasonal variation in water quality of the Gandak River was rendered by seven parameters??turbidity, sulfate, pH, phosphate, water temperature, total alkalinity, and sodium, while total alkalinity and water temperature were responsible for seasonal discrimination in water quality of Ghaghra River. Water temperature, turbidity, total dissolved solids, total suspended solids, calcium, and phosphate were important for seasonal discrimination in water quality of Sone River. The seasonal changes in water quality of the rivers were due to seasonal effects and catchment characteristics. The discriminant functions classified most of the cases correctly.     

Intra-monsoonal variation of zooplankton population in the Sundarbans Estuarine System,India

The present study was conducted during July 2013 (early phase of monsoon or EM) and September 2013 (later phase of monsoon or LM) to ascertain the intra-monsoonal variation on zooplankton, by selecting 15 study stations in the river Saptamukhi, one of the main estuaries in the Sundarbans Estuarine System (SES). In 2013, SES experienced an unusually high monsoonal rainfall also exacerbated by cloud burst event at Himalayan region (upper stretches of SES) which tremendously increased the river runoff. The present work was aimed to decipher the effect of this unusual precipitation during the monsoon season on zooplankton assemblages along with different hydrological parameters. The abundance of zooplankton was recorded as lower during EM compared to LM. Altogether, 56 zooplankton taxa were identified with copepods forming the predominant population. Thirty-three copepod species were reported with 25 calanoid species forming the bulk of the biomass followed by 5 and 3 species of cyclopoids and harpacticoid, respectively. A combination of multivariate cluster analysis, biotic indices, and canonical correspondence analysis revealed noticeable alterations in the zooplankton community structure across the spatio-temporal scale. Furthermore, significant intra-monsoonal changes in zooplankton population correlated with several hydrological parameters were clearly noticed. Paracalanus parvus, Bestiolina similis and Oithona similis were observed to be the most dominant copepod species in both sampling periods. The result of the present study provides new insight on estuarine zooplankton community after unusual rainfall during monsoon season, and provides further evidence to support the conservation and management of the SES ecosystem.