Impacts of inorganic turbidity on diquat efficacy against Egeria densa

In clear water, diquat [6,7-dihydrodipyrido (1,2-1a:2',1'-c) pyrazinediium dibromide] provides excellent submersed Plant control at low concentrations, such as <0.5 mg active ingredient (ai) L-1: however. turbid water conditions can interfere with the activity and effectiveness of this herbicide. Little work has been done to examine what ranges of turbidity caused by different Suspended sediment types affect diquat efficacy against a target species. A growth chamber study was conducted rising diquat against the submersed macrophyte -egeria (Egeria densa Planch.) under a range Of turbid conditions. Two materials were used to create turbid beater conditions: 100% bentonite clay for a "worst-case" scenario and a natural partial-clav (20% clay). Results indicated that a high rate of diquat (2 mg ai L-1) controlled egeria under relatively low levels of turbidity (5-10 NTU) using bentonite clay: however. higher levels (25 to 50 NTU) of turbidity essentially blocked effectiveness of diquat when applied at all rates tested (0.5. 1, 2 mg ai L-1). When using a natural partial-clay sediment, rates of 1 to 2 mg ai L-1 diquat provided good control of egeria in moderately turbid water (15 NTU). Additional evaluations rising different clay types would be useful to determine the effect of inorganic turbidity oil diquat efficacy.

A stochastic model of temporal variations in monthly temperature, precipitation, snowfall, and resulting snowpack

We report a Monte Carlo representation of the long-term inter-annual variability of monthly snowfall on a detailed (1 km) grid of points throughout the southwest. An extension of the local climate model of the southwestern United States (Stamm and Craig 1992) provides spatially based estimates of mean and variance of monthly temperature and precipitation. The mean is the expected value from a canonical regression using independent variables that represent controls on climate in this area, including orography. Variance is computed as the standard error of the prediction and provides site-specific measures of (1) natural sources of variation and (2) errors due to limitations of the data and poor distribution of climate stations. Simulation of monthly temperature and precipitation over a sequence of years is achieved by drawing from a bivariate normal distribution. The conditional expectation of precipitation. given temperature in each month, is the basis of a numerical integration of the normal probability distribution of log precipitation below a threshold temperature (3°C) to determine snowfall as a percent of total precipitation. Snowfall predictions are tested at stations for which long-term records are available. At Donner Memorial State Park (elevation 1811 meters) a 34-year simulation - matching the length of instrumental record - is within 15 percent of observed for mean annual snowfall. We also compute resulting snowpack using a variation of the model of Martinec et al. (1983). This allows additional tests by examining spatial patterns of predicted snowfall and snowpack and their hydrologic implications.

Trophic State Index, morphoedaphic index and fish yield prediction in a sub-tropical lake, Manchar (Sindh), Pakistan

Limnological factors of a sub-tropical lake Manchar were studied on seasonal basis. The mean values of various parameters were: transparency, (secchi disc reading): 90.5 cm, Orthophosphate: 0.257 mg/l, TDS: 3310,5 mg/l, Conductivity: 5232 µs/l, Total Chlorophyll (Planktonic): 31.3 µg/l Planktonic biomass: 5466 µg/l. Trophic state index (TSI) was calculated by using Carlson's (1977) equations. Mean TSI for transparency was 61, while for orthophosphate and chlorophyll, it was 82 and 64 respectively. TSI values indicate advanced eutrophic state of Manchar Lake. Morphoedaphic index (MEI) was also calculated on seasonal basis. The mean values were, TDS: 1103, conductivity: 1744, alkalinity: 60, transparency: 29 and biomass (plankton dry weight): 1746. Fish yield prediction for Manchar Lake (Z =3m, mean area=100 km²) was calculated by using MEI values. The results were quite different among various parameters. Conductivity (89.1mt/y), biomass (67.6 mt/y) and TDS (44.6 mt/y) were found to be good predictors of fish yield. Chlorophyll, transparency and alkalinity values gave very low estimate.

The study of biological characteristic and population dynamic of Caspian vimba (Vimba vimba persa), in coastal waters of Caspian Sea (Mazandaran Province)

This study was conducted to determine reproduction characteristics, diet regime, age structure and population dynamics parameters of the vimba vimba persa (Pallas, 1811) in Mazandaran waters of the Caspian Sea, from October 2008 to September 2009. A total of 994 specimens were monthly collected by beach seine and cast net from six fish landings of Ramsar, Tonekabon, Chaloos, Mahmood Abad, Sari and Behshahr. Biometric characters were measured for each specimen at the laboratory. Scales were used for age determination. Sex determination and fecundity were determined. Population dynamic parameters as well as stock assessment including cohort analysis were estimated using FISAT software. The finding showed that the mean of fork length and body weight of the Caspian Vimba were 168.4±2.6 mm and 71.94±32.24 g respectively. Strong correlation was found between these two variables (a= 0.012; b = 3.047; r2 = 0.955). 92 specimens were studied from the fecundity point of view. This species was found to have more abundance in spring (esp. Apr-May). The samples composed of 397(42.6%) male, 537(57.4%) female; Overall sex ratio (M: F =1: 1.35) was significantly different from the expected 1:1 ratio (p ≤0.05). The advanced stages of maturity (4th & 5th) were found in April and May. The highest Gonadosomatic Index in female was in May and the lowest one was in July. This fish is therefore a spring spawner. The maximum absolute and relative fecundities were 34640 and 260.9, respectively; the minimum absolute and relative fecundities were 5400 and 94.5 respectively. The averages of absolute and relative fecundities were 17198±7710 and 171.85±48.8, respectively. Coefficient vacuity index was 59.2% which indicates that this fish is mesophagous. Among of living creature consumes by Caspian Vimba mollusks, 76 arthropods, worms, plants, detritus and fishes were found 32.9% , 26.7% , 13.4% , 17% , 4.4% and 1.6% respectively. The infinite fork lengths were 261 mm for females, 25mm for males and 261 mm for both sexes respectively. For population growth and mortality parameters; K ( 0.28 per year for both sexes, 0.3 per year for males, 0.33 per year for females); t0 ( -0.65 year for both sexes, -0.23 year in females, -0.51 year in males ); Φ' ( 2.28 ); Z ( 0.98 per year ); M ( 0.59 per year); F ( 0.39 per year) and Exploitation coefficient was 0.4. The analysis showed that total biomass and MSY were 1336 and 528.8 tonnes respectively.