Graham B. McBride

Estimating the sources and transport of nutrients in the Waikato River Basin, New Zealand

North Island of New Zealand. This first application of SPARROW outside of the United States included watersheds representative of a wide range of natural and cultural conditions and water-resources data that were well suited for calibrating and validating the models. We applied the spatially distributed model to a drainage network of nearly 5000 stream reaches and 75 lakes and reservoirs to empirically estimate the rates of nutrient delivery (and their levels of uncertainty) from point and diffuse sources to streams, lakes, and watershed outlets. The resulting models displayed relatively small errors; predictions of stream yield (kg ha � 1 yr � 1 ) were typically within 30% or less of the observed values at the monitoring sites. There was strong evidence of the accuracy of the model estimates of nutrient sources and the natural rates of nutrient attenuation in surface waters. Estimated loss rates for streams, lakes, and reservoirs agreed closely with experimental measurements and empirical models from New Zealand, North America, and Europe as well as with previous U.S. SPARROW models. The results indicate that the SPARROW modeling technique provides a reliable method for relating experimental data and observations from small catchments to the transport of nutrients in the surface waters of large river basins. INDEX TERMS: 1871 Hydrology: Surface water quality; 1803 Hydrology: Anthropogenic effects; 1806 Hydrology: Chemistry of fresh water; 1857 Hydrology: Reservoirs (surface);

Effect of water level fluctuation on nitrogen removal from constructed wetland mesocosms

Nitrogen removal processes were investigated at three frequencies of water level fluctuation, static, low and high (0, 2 and 6 d−1), in duplicate gravel-bed constructed wetland mesocosms (0.145 m3) with and without plants (Schoenoplectus tabernaemontani). Fluctuation was achieved by temporarily pumping wastewater into a separate tank (total drain time ∼35 min). Intensive sampling of the mesocosms, batch-fed weekly with ammonium-rich (∼100 g m−3 NH4-N) farm dairy wastewaters, showed rates of chemical oxygen demand (COD) and total Kjeldahl nitrogen (TKN) removal increased markedly with fluctuation frequency and in the presence of plants. Nearly complete removal of NH4-N was recorded over the 7 day batch period at the highest level of fluctuation, with minimal enhancement by plants. Redox potentials (Eh) at 100 mm depth rose from initial levels of around −100 to >350 mV and oxidised forms of N (NO2 and NO3) increased to ∼40 g m−3, suggesting conditions were conducive to microbial nitrification at this level of fluctuation. In the unplanted mesocosms with low or zero fluctuation, mean NH4-N removals were only 28 and 10%, respectively, and redox potentials in the media remained low for a substantial part of the batch periods (mid-batch Eh ∼+100 and −100 mV, respectively). In the presence of wetland plants, mean NH4-N removal in the mesocosms with low or zero fluctuation rose to 71 and 54%, respectively, and COD removal (>70%) and redox potential (mid-batch Eh>200 mV) were markedly higher than in the unplanted mesocosms. Negligible increases in oxidised N were recorded at these fluctuation frequencies, but total nitrogen levels declined at mean rates of 2.4 and 1.8 g m−2 d−1, respectively. NH4-N removal from the bulk water in the mesocosms was well described (R2=0.97–0.99) by a sorption-plant uptake-microbial model. First-order volumetric removal rate constants (kv) rose with increasing fluctuation frequency from 0.026 to 0.46 d−1 without plants and from 0.042 to 0.62 d−1 with plants. As fluctuation frequency increased, reversible sorption of NH4-N to the media, and associated biofilms and organic matter, became an increasingly important moderator of bulk water concentrations during the batch periods. TN mass balances for the full batch periods suggested that measured plant uptake estimates of between 0.52 and 1.07 g N m−2 d−1 (inversely related to fluctuation frequency) could fully account for the increased overall removal of TN recorded in the planted systems. By difference, microbial nitrification-denitrification losses were therefore estimated to be approximately doubled by low-level fluctuation from 0.7 to 1.4 g N m−2 d−1 (both with and without plants), rising to a maximum rate of 2.1 g N m−2 d−1 at high fluctuation, in the absence of competitive uptake by plants.

The “data-rich but information-poor” syndrome in water quality monitoring

Water quality monitoring conducted routinely over time at fixed sites has been a part of most water quality management efforts for many years. It has been assumed that such monitoring plays a major role in management. However, the lack of routine data analysis, and reporting of information derived from such analysis, points up the fact that the exact nature of the role of routine, fixed-station monitoring is poorly defined.There is a need to very clearly define this role in the design of such systems if routine monitoring is to efficiently and effectively meet the information expectations placed on it. Design of routine monitoring systems will therefore have to consider not only the where, what, and when of sampling, but also why. A framework for including the “why” of monitoring in the design process is proposed and experience with using the framework in New Zealand is discussed.

What do significance tests really tell us about the environment

Routine application of significance tests does not extract the maximum information from environmental data and can lead to misleading conclusions. Reasons leading to this are: a significant result can often be reached merely by collecting enough samples; a statistically significant result is not necessarily practically significant; and reports of the presence or absence of statistically significant differences for multiple tests are not comparable unless identical sample sizes are used. These problems are demonstrated by application to pH data for grazed and retired fields, and by discussion of significance tests used in recent US regulations for groundwater quality. The advantages of equivalence tests, where the tester must state the difference of practical difference, are discussed and applied to the field pH problem. We recommend that environmental managers and scientists pay more attention to statistical power and decide on what is a practical difference. Confidence intervals for the size of the differences, accompanied where necessary by equivalence tests, are the preferred means of addressing the question: “is there a difference of practical significance?”

Large-scale freshwater microbiological study: rationale, results and risks

A fifteen-month fortnightly survey of microbial health risk indicators and pathogens has been carried out at 25 freshwater recreational and water supply sites distributed throughout New Zealand, for: E. coli, Clostridium perfringens spores, F-RNA bacteriophage, somatic coliphage, human enteroviruses, human adenoviruses, Cryptosporidium oocysts, Giardia cysts, Salmonella and Campylobacter. Sites were selected to represent five geographical areas covering New Zealand and five categories of predominant environmental impact: birds, dairy farming, forestry/undeveloped, municipal, and sheep/pastoral farming. Six of the sites were also source waters for treated drinking-water supplies. Of the indicators, E. coli was detected in 99 % of all samples, with somatic coliphage being detected most of the time (89 %). Of the pathogens tested, Campylobacter and human adenoviruses were inferred to be the most likely to cause human waterborne illness to recreational freshwater users. Using data from all sites, an estimated 5 % of notified campylobacteriosis cases in New Zealand could be attributable to water contact recreation. The critical value for E. coli as an indicator of increased Campylobacter infection is in the range of 200-500 E. coli per 100 ml. This result has been used to derive new national water quality guidelines for recreational fresh water in New Zealand.

Modelling biofilm nitrogen transformations in constructed wetland mesocosms with fluctuating water levels

A mathematical model has been developed that attempts to reproduce patterns of nitrogen removal observed in experiments investigating constructed wetland treatment of ammonium-rich wastewaters under a range of frequencies of water level fluctuation. The experiments were carried out using batch-fed gravel-filled mesocosms, with and without plants, subjected to fluctuating oxygen input through a drain-and-refill regime. Experimental data showed that removal of ammoniacal-nitrogen (NH4–N) and chemical oxygen demand (COD) increased markedly with fluctuation frequency. Plants also tended to enhance the removal of NH4-N and COD. For the highest fluctuation frequency (16 cycles per day, plants absent), accumulation of oxidised nitrogen (NOx–N) was observed to continue even when the wastewater NH4–N had disappeared from solution. A process-based numerical model was developed to elucidate the strength of competing nitrogen transformation processes, which were postulated to be strongly influenced by biofilms and adsorption/desorption associated with gravel surfaces and organic matter, particularly when the mesocosm was empty and liquid on the biofilms was exposed to the atmosphere. A combination of thin-biofilm theory, the microbiological kinetics in the IAWQ activated sludge model No. 2, reversible sorption kinetics and mixing equations was used to demonstrate that very rapid initial decreases in NH4–N were likely to be caused by adsorption onto the gravel and that during the latter part of the batch periods nitrification was likely to be controlled by the rate of desorption of this NH4–N. Nitrification could therefore continue when NH4–N was almost absent from the bulk water. At moderate-to-high fluctuation frequencies (≥6 cycles per day) the presence of plants enhanced NH4–N removal and NOx–N accumulation, through a combination of direct uptake of NH4–N and increased root-zone reaeration.

Applications: Equivalence Tests Can Enhance Environmental Science and Management

Tests of point hypotheses are common in observational environmental studies, but there is concern about their appropriateness. Exhortations to restrict sample sizes on the basis of a power analysis for such tests may fail to satisfy the environmental professional, because sample sizes are not always easily controlled. Testing of interval hypotheses via equiva-lence test procedures offers a way of testing meaningful hypotheses and of giving effect to the precautionary principle. An example is given which concerns mining impacts on stream benthic invertebrate communities, and includes calculation of Bayesian posterior probabilities.

WATER QUALITY IN A POLLUTED LOWLAND STREAM WITH CHRONICALLY DEPRESSED DISSOLVED OXYGEN : CAUSES AND EFFECTS

Abstract The Whangamaire Stream (North Island, New Zealand) has high concentrations of nitrate nitrogen (NO− 3‐N), biochemical oxygen demand (BOD5), and Kjeldahl nitrogen (TKN) as a result of catchment land use practices. The lower reaches of the stream drain intensively farmed land and have dissolved oxygen (DO) levels of 10–50% saturation. The dominant riparian vegetation, Apium nodiflorum, provides a large organic loading by intercepting nutrients in run‐off and then decaying in the stream channel. Water quality and reaeration aspects of the stream were studied in order to explain the observed low DO levels. Measurements of the reaeration coefficient at 20°C, K2 20, using methyl chloride (CH3Cl) as a gas tracer, yielded values of 1.1–3.0 d−1 for the upper part of the study reach and 15.5–16.2 d−1 for the lower reach (overall average 12.5 ± 2.5 d−1). These were in agreement with values inferred from single‐station diurnal curve analysis, which also showed that respiration was dominant in the lower reach...

River water quality trends and increased dairying in Southland, New Zealand

Abstract Trends in six water quality variables measured at 29 Southland, New Zealand, freshwater sites between July 1995 and June 2001 have been assessed. These are compared to changes in livestock numbers to assess whether water quality changes could have been driven by the intensification and expansion of dairy farming and/or by other pressures. Trends were assessed for raw and for flow‐adjusted data, the latter being a better indicator of effects of changing external pressures on water quality (an observed water quality trend may be merely the result of changes in river flow). Results indicate that increased dairy farming has been associated with increasing concentrations of dissolved reactive phosphorus. There has been a worsening in other water quality variables (oxidised nitrogen, dissolved oxygen) but these also occurred in non‐dairying catchments. An improvement in observed water clarity disappeared after flow adjustment. Continued monthly water quality monitoring is necessary to watch for emerging trends.

Trends in New Zealand's National River Water Quality Network

Abstract An analysis of trends was made for the 14 physical/chemical determinands measured monthly over the period 1989–93 at 77 river sites distributed throughout New Zealands North and South Islands. This has used non‐parametric Kendall slope estimators and associated tests, accounting for seasonality, which have been applied to both the raw data and to flow‐adjusted data (flows in much of the North Island trended downward over the period). Results indicate a general improvement in water quality, particularly in the South Island. Downward national trends, for both raw and flow‐adjusted data, were found for water temperature, BOD5, NH4‐N, NOx‐N and TP. Upward national trends, again for both raw and flow‐adjusted data, were found for dissolved oxygen, visual clarity, conductivity, and g340/g440 (indexes of dissolved colour). No national trends are reported for pH or DRP. Downward trends for turbidity and TN were seen in the raw data only. A general characterisation of the dependence of these determinands...