Aslan E. Wright-Stow

Trends in water quality of five dairy farming streams in response to adoption of best practice and benefits of long-term monitoring at the catchment scale

Five streams in catchments with pastoral dairy farming as the dominant land use were monitored for periods of 7–16 years to detect changes in response to adoption of best management practices (BMPs). Stream water quality was degraded at the start with respect to N, P, suspended solids (SS) and E. coli concentrations, and was typical of catchments with intensive pastoral agriculture land use. Trend analysis showed a decrease in SS concentration for all streams, generally increasing water clarity, and lower E. coli concentrations in three of the streams. These are attributed to improved stream fencing (cattle exclusion) and greater use of irrigation for treated effluent disposal with less reliance on pond systems discharging to streams. Linkages between water quality and farm actions based on survey data were used to develop BMPs that were discussed at stakeholder workshops. Generic and specific BMPs were developed for the five catchments. The 3–7 year periodicity of major climate cycles, as well as market forces and a slow rate of farmer adoption of simple BMPs mean that monitoring programs in New Zealand need to be much longer than 10 years to detect changes caused by farmer actions. Long-term monitoring is also needed to detect responses to newly legislated requirements for improved water quality.

Trophic basis of production for a mayfly in a North Island, New Zealand, forest stream: Contributions of benthic versus hyporheic habitats and implications for restoration

Abstract The leptophlebiid mayfly Acantho‐phlebia cruentata (Hudson) is restricted to the North Island and some associated offshore islands of northern New Zealand where it commonly occurs in benthic and hyporheic habitats of forested streams. We investigated: (1) life history; (2) secondary production in benthic and hyporheic habitats; and (3) major energy sources contributing to nutrition and production of this species in a pristine forest stream. Most nymphal size classes were present throughout the year, and emergence extended over several months, peaking from February to April. Despite apparently having extended emergence and recruitment periods, Acanthophlebia exhibited a predominantly univoltine life history. Annual benthic production (calculated by the size‐frequency method) was 0.318 g dry mass (DM) m–2 year–1, compared to 4.601 g DM m–2 year–1 in high‐density benthic habitats at the tails of pools, and 34.476 g m–3 year–1 for colonisation baskets set at 15–45 cm deep in the substratum. On a habitat weighted basis averaged out over the entire sampling reach, it was estimated that 76% of annual production occurred in hyporheic habitats >10 cm below the streambed surface. Gut contents were dominated by fine particulate matter (FPM) ≤75 μm and larger inorganic material on all dates in individuals from both benthic and hyporheic habitats. Fungi were relatively abundant in guts of benthic animals collected on some dates, whereas spores and pollen were relatively common food items in both habitats on occasions. Analysis of the trophic basis of production, based on gut contents and assumed assimilation and net production efficiencies, indicated that benthic secondary production was supported largely by fungi (48% of production) and FPM (37%), whereas FPM supported a higher level of hyporheic production (52%) than fungi (27%). Although stable carbon isotope values suggested dependence on epilithon, the enriched δ15N values for this food source implicated the involvement of a microbial loop whereby a substantial proportion of Acanthophlebia nutrition appeared to be derived from heterotrophs growing in FPM and epilithon that had assimilated dissolved organic carbon. This study has highlighted the significant role that hyporheic habitats can play in the ecology of Acanthophlebia populations in pristine native forest streams. Re‐establishment of hyporheic function would appear to be an important component of stream restoration work to enable the successful recolonisation of Acanthophlebia populations at sites where they historically occurred.

Volunteer stream monitoring: Do the data quality and monitoring experience support increased community involvement in freshwater decision making?

Recent freshwater policy reforms in New Zealand promote increased community involvement in freshwater decision making and management. Involving community members in scientific monitoring increases both their knowledge and their ability to discuss this knowledge with professionals, potentially increasing their influence in decision-making processes. However, these interactions rarely occur because, in particular, of perceptions that volunteer-collected data are unreliable. We assessed the agreement between volunteer (community group) and local government (regional council) data at nine stream sites across New Zealand. Over 18 months, community groups and regional council staff monitored, in parallel, a common set of water quality variables, physical habitat, periphyton and benthic macroinvertebrates that are routinely used by regional councils for statutory state of environment reporting. Community groups achieved close agreement (correlations ≥ 0.89, bias < 1%) with regional councils for temperature, electrical conductivity, visual water clarity, and Escherichia coli. For dissolved oxygen, nitrate, and pH, correlations were weaker (0.2, 0.53, and 0.4, respectively). Volunteer assessments of physical habitat were as consistent over time as those of councils. For visual assessments of thick periphyton growths (% streambed cover), volunteers achieved a correlation of 0.93 and bias of 0.1% relative to councils. And for a macroinvertebrate biotic index that indicates water and habitat quality, correlation was 0.88, bias was < 5%, and the average difference was 12% of the index score. Volunteers showed increased awareness of local freshwaters, understanding of stream ecosystems, and attentiveness to local and national freshwater issues. Most volunteers had shared their knowledge and interest with others in their community. Most groups had developed relationships with their regional council, and some volunteers became more interested in engaging in freshwater decision making. Given adequate professional support, community-based water monitoring can provide data reliable enough to augment professionally collected data, and increase the opportunities, confidence, and skills of community members to engage in freshwater decision making.

Managing pollutant inputs from pastoral dairy farming to maintain water quality of a lake in a high-rainfall catchment

A study (2004–11) of a dairy catchment stream entering an oligotrophic lake in an area of very high rainfall (~5 m year–1) yielded median concentrations of total nitrogen (TN), total phosphorus (TP), suspended sediment (SS) and Escherichia coli (E. coli) of 0.584, 0.074 and 3.7 g m–3, and 405/100 mL (most probable number method), respectively. Trend analysis indicated significant (P < 0.01) decreases for TN (–0.08 ± 0.02 g m–3 year–1), TP (–0.01 ± 0.005 g m–3 year–1) and SS (–0.45 ± 0.14 g m–3 year–1) and were partly attributable to improved exclusion of cattle from the stream. Water balance calculations indicated that approximately one-half the rainfall left as deep drainage that by-passed catchment outlet flow recorders. Estimates of catchment yields for TN were improved by taking into account groundwater hydrology and concentrations from well samples. Storm-flow monitoring inflows exceeding the 97.5th percentile contributed ~40% of total loads leaving the catchment so that specific yields for SS, TN and TP augmented by groundwater inputs and storm flows were ~960, 45 and 7 kg ha–1 year–1, respectively. These compared well with modelled results for losses from dairy farms in the catchment of 40–60 kg N ha–1 year–1 and 5–6 kg P ha–1 year–1 and indicated that attenuation losses were relatively small.

Sedimentation effects on the benthos of streams and estuaries: a cross-ecosystem comparison

Connected ecosystems can be detrimentally affected by the same stressor, such as occurs when excess fine sediment moves from streams into estuaries. However, no previous study has directly compared sedimentation effects across these ecosystems. Responses of benthic macroinvertebrate communities to sedimentation were predicted to vary between streams and estuaries, because of intersystem differences in the physical environment and representation of species traits. To compare these responses, fine terrigenous sediment was added simultaneously to replicated plots in stream-run habitats and the adjacent estuary. Although sediment addition to streams caused reduced invertebrate densities after 1 week, no changes in taxon richness or consistent changes in community structure were detected, and densities had recovered another week later. In contrast, sediment addition to estuarine sites caused large declines in invertebrate densities and changes in community structure, which remained evident at the innermost sites 16 days after addition. Across both systems, sedimentation effects were detectable only for some of the common taxa, and biological traits were not predictive of effects. The potential for more severe effects in estuaries should be considered when predicting the implications of land-use changes that may increase sedimentation, and when setting guidelines for maintaining stream and estuarine condition.

Responses of stream macroinvertebrate communities and water quality of five dairy farming streams following adoption of mitigation practices

ABSTRACT Five streams in catchments with pastoral dairy farming as the dominant land use were monitored for periods up to 13 years after adoption of mitigation practices (MPs) to detect changes in stream macroinvertebrate communities and water quality. Water quality and macroinvertebrate community condition was degraded at the start with respect to N, P, suspended solids (SS), Escherichia coli concentrations, and a number of macroinvertebrate metrics, and were typical of catchments with intensive pastoral land use. Trend analysis showed a decrease in SS concentrations for all streams, generally increasing water clarity, and lower E. coli concentrations in two streams. The improvements, attributable to improved stream fencing and effluent disposal, were only sometimes associated with improved macroinvertebrate metrics, and suggest constraints of connectivity, habitat, time, and/or MP effectiveness. Macroinvertebrate species composition had the strongest correlation with total nitrogen at two sites, but changes probably reflected indirect factors associated with TN concentrations were responsible.

Water quality and benthic macroinvertebrate communities in karst landscapes of North Island, New Zealand: influences of water sources, habitat type and anthropogenic disturbances

Abstract In karst landscapes, aquatic habitats differ in terms of the relative contributions of different water sources (allogenic surface stream vs autogenic karst groundwater) and their geomorphology. Benthic macroinvertebrate community structure in these habitats is likely to vary in response to this heterogeneity, as well as to the physicochemical differences between water flowing through pasture vs native forest dominated catchments. Surveys were conducted to examine the influences of water source, habitat type (main stream-ways and side passages in caves, and epigean springs) and surrounding land use (native forest or pasture) on the water quality and benthic community structure in the Maniapoto Karst, North Island, New Zealand. Generally, springs and cave side passages received more autogenic water, indicated by lower temperatures and higher conductivities, than the main stream-ways of caves. However, in terms of community structure, the epigean springs and cave side passages were most distinct from each other, whilst the main stream-ways of caves were intermediate between the other two habitats. Temperature and nitrate concentrations were higher in sites surrounded by pasture than those in native forest, but surrounding land use exerted less influence on macroinvertebrate community structure than habitat type. A comparison of community structure in caves with high and low tourist traffic failed to identify any significant effects.