John W. Nagels

Inactivation of faecal indicator micro-organisms in waste stabilisation ponds: interactions of environmental factors with sunlight

Sunlight exposure is considered to be the most important cause of “natural” disinfection in waste stabilisation ponds (WSPs). We examined the influence of dissolved oxygen (DO), pH, and particulate and dissolved constituents in WSP effluent, on sunlight inactivation of faecal micro-organisms, using small reactors operated under controlled physico-chemical conditions. Inactivation of both enterococci and F-RNA phages increased strongly as DO was increased, and also depended on light-absorbing pondwater constituents, but pH was not influential over the range investigated (7.5 to 10). Inactivation of E. coli increased strongly when pH increased above 8.5, as well as being strongly dependent on DO. Inactivation of F-DNA phage was independent of the factors investigated. These results are consistent with the F-DNA phages being inactivated as a result of direct DNA damage by UVB in sunlight, whereas the other three microbiological indicators are inactivated as a result of photo-oxidative damage, although the target of damage is apparently different. Our findings of diverse influences of physico-chemical conditions suggest difficulties in interpreting data for a single micro-organism to indicate WSP effluent quality. However, sunlight remains the factor of over-riding importance, and disinfection in WSPs may be enhanced by increasing sunlight exposure.

Water quality of a lowland stream in a New Zealand dairy farming catchment

Abstract A small stream in a predominantly dairying catchment in the Waikato region of New Zealand was monitored for 2 years at three sites. Total nitrogen (TN) concentrations were up to 7.09 g m‐3 in winter, with the bulk comprising nitrate nitrogen (NO‐ 3‐N). During summer NO‐ 3‐N was near zero and TN mostly comprised organic nitrogen. Maximum concentrations of total phosphorus (TP) and dissolved reactive phosphorus (DRP) were 1.64 and 0.555 g m‐3, respectively, and peaks coincided with spring and autumn applications of phosphorus fertiliser. Ammoniacal nitrogen concentrations exceeded 1 g m‐3 on several occasions and mean concentrations at the three sites were 0.165–0.272 g m‐3. Faecal coliform and enterococci bacteria concentrations were 64–26000 and 7–23000 cfu per 100 ml, respectively. Specific yields of TN and NO‐ 3‐N (35.3 and 30.7 kg ha yr‐1, respectively) were much greater than any previously reported for New Zealand pasture catchments, whereas TP and DRP yields (1.16 and 0.54 kg ha yr‐1, respec...

Water quality impact of a dairy cow herd crossing a stream

Abstract The water quality impact of a herd of 246 dairy cows crossing a stream ford was documented. Two cow crossings produced plumes of turbid water associated with very high concentrations of faecal indicator bacteria (Escherichia coli) and high suspended solids (SS) and total nitrogen (TN). On the first crossing, towards the milking shed, the cows were tightly‐bunched and produced a sharp spike of contamination (E. coli peaking at 50 000 cfu/100 ml). After milking, the cows wandered back across the stream as individuals or small groups, and contaminants were less elevated, albeit for a longer period. Light attenuation, measured continuously by beam transmissometer, correlated closely with E. coli, SS, and TN, permitting the total yield of these contaminants to be estimated. Contaminant yields for the two crossings were very similar, suggesting that time taken and whether or not cows are herded may not greatly influence water quality impact. The cows defecated c. 50 times more per metre of stream crossing than elsewhere on the raceway. This study has shown that cattle accessing stream channels can cause appreciable direct water contamination, suggesting that excluding cattle from streams will have major water quality benefits.

The influence of aquatic macrophytes on the hydraulic and physico-chemical properties of a New Zealand lowland stream

The effects of macrophytes on hydraulic and physico-chemical variables were examined by conducting tracer experiments with SF6, CH3Cl and rhodamine WT in a stream before and after complete removal of plants from a 180 m reach. Whakapipi Stream has high average biomasses (up to 370 g dw m-2) of macrophytes (predominantly Egeria densa) that, on average, cause summer velocities to be lowered by 30% and depths increased by 40%, compared to a plant-free channel. Mannings roughness coefficent was consistently higher by 0.13 and longitudinal dispersion coefficients were more variable (CV = 52%, cf. 20% when plants removed), when macrophytes were present. Stream dissolved oxygen (DO) and temperatures were unevenly distributed, possibly as a result of transient storage zones attributable to plant biomass. Surface water in macrophyte patches was 1-5 °C warmer than water in channels or beneath the plants near the bed of the stream, and DO was 2-28% of saturation higher at the top of the plants than in channel water and up to 7% higher than in bottom water. Effects of increased small-scale turbulence on the reaeration coefficient, K2(20), were cancelled by increased stream depth and reduced velocity so that it varied little with flow. Application of a single-station diurnal curve model, DOFLO (Dissolved Oxygen at Low Flow), to continuous monitoring data gave values of K2(20) in broad agreement with those measured by the gas tracer method and showed that rates of gross photosynthetic production in daylight (10-27 g m-2 d-1) and respiration at 20 °C (19-37 g m3 d-1) were high by comparison with other rural streams. Streams with smaller K2(20) values than Whakapipi Stream but with similar levels of productivity and community respiration would show more pronounced diurnal variations in DO and even be anoxic at times.

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...

Algal abundance, organic matter, and physico‐chemical characteristics of dairy farm facultative ponds: Implications for treatment performance

Abstract Six Waikato (New Zealand) dairy farm facultative ponds (DFPs), which met the larger sizes specified in recent dairy industry guidelines, were sampled monthly over an annual period. Median wastewater BOD5 was 65 g m‐3, suspended solids (SS) 206 g m‐3, ammoniacal N 37 g m‐3, total nitrogen 69 g m‐3, and faecal coliforms 24 000 (100 ml)‐1. This was 20–70% better than reported for DFPs built to previous guidelines, except for SS levels which were within reported ranges. However, performance was highly variable and only ½ of the DFPs studied consistently met an effluent standard of ≤ 100 g m‐3 BOD 5 and only one reached ≤ 150 g m‐3 SS. Removal of BOD 5 was much lower than recorded for SFPs in New Zealand with equivalent BOD 5 loading. Although the mean euphotic depth was only 0.11 m, algal biomass in DFPs was similar to that recorded for SFPs. Low phaeophytin concentrations and daytime oxygen exceeding 200% saturation in the shallow epilimnion on sunny days suggested a relatively healthy photosynthetic algal population was present in the DFPs. However, wastewater entering DFPs showed high median COD levels (1420 g m‐2). COD:BOD 5 ratios of c. 12.1 (compared with 1.5–1.8 for SFPs) and BOD 10 :BOD 5 ratios of c. 2 indicated the presence of a large pool of slowly degradable organic matter in the wastewater. This resulted in sustained exertion of BOD in the pond, explaining the “apparent” poor removal of BOD 5 by DFPs. Conductivity was found to be a useful single‐measure indicator of overall pond performance and management of sludge levels in the preceding anaerobic pond was identified as a key factor affecting DFP performance. Further improvements in dairy farm stabilisation pond performance are likely to be required on many farms to meet receiving water guidelines for the protection of water quality and aquatic life.

Controlled release experiments to determine the effects of shade and plants on nutrient retention in a lowland stream

Understanding nutrient uptake and retention in streams remains an important challenge for lotic scientists. In this study a series of pulse and continuous releases of dissolved nutrients were made to shaded and unshaded (reference) reaches of a small lowland stream to determine whether suppression of macrophyte growth by riparian shade impaired nutrient retention. The nutrients were dissolved reactive phosphorus (DRP), total ammoniacal nitrogen (NH4–N) and nitrate nitrogen (NO3–N). Nutrient reductions ranged from 100% of DRP when stream water was anoxic, to 5–10% for NH4–N and NO3–N in the reference reach. Nutrient removals were affected by travel times in each reach. Percentage removals of NH4–N (46 ± 10) and NO3–N (52 ± 14) were higher in the shaded reach than in the swifter moving reference reach (15 ± 8 and 16 ± 10, respectively). DRP (%) removals were 75± 7 and 57 ± 12 for the shaded and reference reaches, respectively. The presence of emergent marginal macrophytes (Persicaria hydropiper) increased stream velocity in the reference reach by reducing the effective channel cross-section area. Shading reduced plant biomass, increased the channel cross-section and lowered velocity in the experimental reach, effecting dramatic reductions in nutrient concentrations over short distances. The opposite effect is more typical for larger, swifter streams having dense stands of submerged macrophytes, where lowering channel plant biomass will cause increased velocities and lower relative nutrient losses. Riparian shade does not necessarily impair nutrient uptake from small streams. Where invasive marginal species such as P. hydropiper dominate headwater streams shade may be beneficial to the protection of downstream waters from eutrophication. Where reduction of nutrient fluxes from small streams is a key objective for protection of downstream waters, active management of streams should seek to increase travel times, allowing greater potential for nutrient uptake. This will need to be weighed against the need for effective drainage in pastoral areas where reduced travel times are usually sought.

Microbial Transport, Retention, and Inactivation in Streams: A Combined Experimental and Stochastic Modeling Approach

Long-term survival of pathogenic microorganisms in streams enables long-distance disease transmission. In order to manage water-borne diseases more effectively we need to better predict how microbes behave in freshwater systems, particularly how they are transported downstream in rivers. Microbes continuously immobilize and resuspend during downstream transport owing to a variety of processes including gravitational settling, attachment to in-stream structures such as submerged macrophytes, and hyporheic exchange and filtration within underlying sediments. We developed a stochastic model to describe these microbial transport and retention processes in rivers that also accounts for microbial inactivation. We used the model to assess the transport, retention, and inactivation of Escherichia coli in a small stream and the underlying streambed sediments as measured from multitracer injection experiments. The results demonstrate that the combination of laboratory experiments on sediment cores, stream reach-scale tracer experiments, and multiscale stochastic modeling improves assessment of microbial transport in streams. This study (1) demonstrates new observations of microbial dynamics in streams with improved data quality than prior studies, (2) advances a stochastic modeling framework to include microbial inactivation processes that we observed to be important in these streams, and (3) synthesizes new and existing data to evaluate seasonal dynamics.

Effects of forest harvesting and woody debris removal on two Northland streams, New Zealand

Abstract The short‐term effects of Pinus radiata forest harvesting to the stream edge followed by stream‐cleaning (removal of woody debris from the stream channel), on instream light levels, stream temperature, dissolved oxygen concentrations, and aquatic invertebrates were assessed in streams draining partly (25% clear‐cut) and totally (100% clear‐cut) harvested catchments, compared with nearby indigenous forest and mature pine plantation reference sites. There were marked increases in in‐stream light levels and water temperatures following forest harvest and stream‐cleaning at both sites. In‐stream light levels increased from 8–13% to 60–90% and maximum monthly water temperatures increased on average by 5.6°C in the partly harvested and 3.6°C in the fully harvested catchment. Dissolved oxygen levels decreased at both sites shortly after harvest (94%‐71% saturation in the partly harvested catchment; 72%‐37% saturation in the totally harvested catchment), increasing to 75% and 81%, respectively, 1 year later. Although aquatic invertebrate mean density and taxa richness increased at both sites following harvest, the relative abundance of sensitive mayfly, caddisfly, and stonefly species decreased and community composition changed to one dominated by Chironomidae (midges) or Mollusca. Impacts relative to pre‐harvest conditions were not as marked in the totally harvested catchment, possibly because of pre‐existing elevated stream temperatures and high levels of sand and silt. Any downstream protection provided by the forested headwaters of the partly harvested catchment was soon lost after the stream entered the clear‐cut area, although these forested headwaters may provide a potential source of aquatic invertebrates for re‐colonisation in the future as water quality and habitat recover. Our results suggest that: (1) pre‐existing constraints on habitat quality can influence the magnitude of harvesting impacts; and (2) length of stream edge harvested may be a better indicator of impact on some aspects of stream ecology, such as lighting, stream temperature, dissolved oxygen, and aquatic invertebrate community composition, than percentage of catchment harvested. This study also highlights the importance of considering the hydro‐logical and landscape context for mitigating harvesting and wood management impacts on stream ecosystems.

Differential behaviour of Escherichia coli and Campylobacter spp. in a stream draining dairy pasture

The faecal indicator bacterium Escherichia coli and thermotolerant Campylobacter spp., which are potentially pathogenic, were investigated in the Toenepi Stream draining a pastoral catchment dominated by dairying. Bacteria concentrations were monitored routinely at fortnightly intervals over 12 months and intensively during storm events to compare the transport dynamics of bacterial indicator and pathogen under varying hydro-meteorological conditions. Routine monitoring indicated median concentrations of 345 E. coli MPN 100 ml(-1) and relatively low concentrations of 2.3 Campylobacter MPN 100 ml(-1). The bacterial flux was three orders of magnitude greater under elevated stream flow compared with base-flow. E. coli peak concentrations occurred very close to the turbidity peak and consistently ahead of the Campylobacter spp. peak (which was close to the hydrograph peak). We postulate that, under flood conditions, the E. coli peak reflects the entrainment and mobilisation of in-stream stores on the flood wave front. In contrast, Campylobacter spp. are derived from wash-in from land stores upstream and have travelled at the mean water velocity which is slower than the speed of the flood wave. Our findings of different dynamics for E. coli and Campylobacter spp. suggest that mitigation to reduce faecal microbial impacts from farms will need to take account of these differences.