Water quality in New Zealand rivers: current state and trends

River water quality, particularly in lowland catchments, is a matter of concern to the New Zealand public. We assessed river water quality and biological state and trends using data from more than 900 monitoring sites. Parallel state and trend analyses were carried out using all sites and a subset of lowland river sites. Median water-quality state in urban and pastoral land-cover classes was poorer than in exotic forest and natural land-cover classes, and lowland sites in the urban and pastoral classes had the poorest water quality. Nutrient and Escherichia coli concentrations increased and visual clarity and Macroinvertebrate Community Index scores decreased as proportions of catchments in high-intensity agricultural and urban land cover increased. Ten-year trends (2004–2013) indicated recent improvements in ammoniacal nitrogen, dissolved reactive phosphorus and total phosphorus in the pastoral and urban classes, possibly reflecting improved land management. In contrast, trends in nitrate-nitrogen in the exotic forest and cool-dry/pastoral classes indicated worsening conditions.     

Transverse mixing and surface heat exchange in the Waikato River: A comparison of two models

Abstract

Two mathematical models of different complexity were used to study transverse dispersion and surface heat transfer in the lower Waikato River. A simple analytical streamtube model (HPLUME) gave adequate temperature predictions in a reach where the channel was fairly regular but performed poorly where there were extensive shallows. In the latter reach, a two‐dimensional numerical model (SYSTEM21) gave good temperature and flow predictions once properly calibrated. Model calibration proved to be difficult in the Waikato River because the natural river temperature varied significantly along the channel. A search method was developed to estimate both the transverse dispersion and surface heat exchange coefficients from measured plume temperature profiles based on the observation that transverse variations in natural temperature were small. This method was used to calibrate SYSTEM21 in two separate reaches. Coefficient estimates were sensitive to measurement errors and slight departures in homogeneity of natural temperature and it would be desirable to corroborate the estimates of E_z using dye tests. In the upper reach, the average transverse dispersion coefficient was E_z/hu? = 1 which is high but within the range of published values. A sharp bend and buoyant spreading contributed to the high E_z value. E_z increased with river flow because both h and u? increase with flow. In the lower reach, E_z/hu? = 0.1 which is lower than expected but islands may have affected the model calibration. The surface heat exchange coefficient averaged K = 84–167 W m^?2 s^?1 °C^?1 which falls within the range of published values. No significant relationship could be found between surface heat exchange coefficient and meteorological variables.     

珠江口水域化学耗氧量、溶解氧、无机磷与有机磷的三维水质数学模拟

珠江沿岸城市排污量大,对污染源治理能力十分有限,大量污染物通过河流或直接排放到珠江口,河口区半封闭的地形及潮水顶托使得污染物不易输送出外海,致使珠江口水质恶化,原有海洋生态环境遭到破坏,反过来制约了经济的发展.     

Skewed Water Temperature Occurrence Frequency in the Sea off Sanriku, Japan, and Intrusion of the Pure Kuroshio Water

Temperature and salinity data obtained by the Iwate Fisheries Technology Center were analyzed for the period 1971–1995. It was found that occurrence frequency distributions of temperature and salinity are very skewed at depths deeper than 200 m and that temperature sometimes exceeds m + 5σ (m: mean and σ: standard deviation. If such abnormally high temperatures are real the 3σ criterion cannot be adopted. Oceanic conditions were surveyed in 1972 and 1979, when temperatures exceeding m + 5σ were observed. It was found that the abnormally high temperature (and high salinity) water was the pure Kuroshio Water introduced into the region due to some special conditions such as abnormal approach of large warm-core ring to the Sanriku Coast or abnormal northward extension of the Kuroshio along the coast. These events are very rare, occurring only twice in the 25-year period analyzed, but the abnormally high temperature observed is real. This revised version was published online in July 2006 with corrections to the Cover Date.