Spot sampling of nutrient concentrations in the Puarenga catchment, Rotorua

The Centre for Biodiversity and Ecology Research was approached by Tūhourangi Tribal Authority for assistance with measuring water quality in streams in the Puarenga Stream catchment. Water sampling was subsequently undertaken on 18 July 2011 and samples were analysed to determine concentrations of total and dissolved fractions of nitrogen and phosphorus. Nitrogen and phosphorus are both essential plant nutrients which, when present in excess, can cause eutrophication and associated water quality decline of freshwaters. High concentrations of dissolved forms of nitrogen can also be toxic to aquatic organisms. Excessive nitrogen and phosphorus concentrations are typically the result of pollution due to human activities, although groundwater in the Central Volcanic Plateau region can have elevated concentrations of phosphorus arising from natural geological sources. This report summarises the methods used, presents the results and places measured concentrations in context by drawing comparisons with both guideline and regional mean values

Variability in nutrient loading to lake ecosystems and associated impacts on water quality

Globally, the accelerated eutrophication of lake ecosystems due to excess inputs of nitrogen (N) and phosphorus (P) is a significant problem. The rate of loading of N and P to lakes varies both in space and time; consequently, developing good understanding of such spatial and temporal variability is critical for developing integrated approaches to managing lake water quality. This study aimed to improve understanding of spatial and temporal variations in N and P loading to lakes, and, to examine how this variability affects water quality. The topic was considered at global, national and catchment scales. Analysis of an extensive global dataset was undertaken to examine relationships between N, P and chlorophyll a (chl a) in lakes along a gradient of latitude inclusive of tropical, temperate and polar regions. The ratio of total nitrogen (TN) to total phosphorus (TP) was positively correlated with latitude, reflecting global–scale variation in nutrient cycling processes and/or nutrient sources. Relative to temperate lakes, the statistical capability of concentrations of TN and TP to predict chl a concentration (i.e. indicating bottom–up control by nutrients) was shown to be poor for both tropical and polar lakes. These differences reflected latitudinal variation in lake ecosystem functioning, and highlighted the potential unsuitability of applying relationships derived for temperate lakes elsewhere. Quantile regression was used to derive theoretical chl a near–maxima as a function of either TN or TP concentrations. Consequently, chl a:TN and chl a:TP yields (by mass) of 0.046:1 and 0.87:1 were determined to approximate the maximum possible yields of chl a under optimal conditions as a proxy for phytoplankton biomass potential. Nationally–significant relationships between landscape characteristics and in–lake TN and TP concentrations were quantified for a representative sample of 101 lakes in New Zealand. Geographical Information Systems were used to analyse data from a range of sources that related to both lake–specific and wider landscape characteristics. Inferential statistical methods were then used to quantify relationships between in–lake nutrients and both land use and naturally–occurring soil P. National–scale variability in mean catchment soil P was found to be unrelated to in–lake TP concentrations, reflecting the dominant influence of human–related sources of P on TP concentrations in New Zealand lakes. The extent of intensive pastoral agriculture was the best land use predictor of TN and TP concentrations, accounting for 38.6% and 41.0% of variation respectively. Exotic forestry accounted for a further 18.8% of variation in TP concentrations. A sub–sample of lakes for which intensive pastoral agriculture was the dominant catchment land use was then considered to test hypotheses regarding potential interactive effects of eight landscape characteristics on the positive relationship between intensively managed pasture and in–lake nutrient concentrations. Both maximum lake depth and the ratio of catchment to lake area had significant interactive effects, exerting a negative and a positive influence, respectively. In addition, an indicator of hydrological connectivity (lake order) also had a positive interactive effect on the relationship between this land use type and in lake TP (but not TN) concentrations. To examine these broad relationships at finer spatial resolution, and also to quantify temporal variations in nutrient loading, an extensive field programme was conducted in the catchment of Lake Rotorua (Bay of Plenty, New Zealand); a large (80.5 km2), relatively shallow (zmean = 10.8 m) lake that has experienced eutrophication. The Ngongotaha and Puarenga streams are two major inflows to the lake that were sampled at high frequency throughout a wide range of stream discharge coinciding with rainfall events. Both streams had different catchment characteristics (e.g. land use and hydrogeomorphology) which enabled spatial variations in nutrient loading between sub–catchments located upstream of a common lake ecosystem to be examined. Streams were sampled during a total of 17 hydrological events, including three during which both streams were simultaneously sampled to compare differences in pollutant transport between the streams during similar hydrological conditions. Relationships between nutrient concentrations and stream discharge were broadly similar for the two catchments, and quantification of relationships permitted nutrient loading to be estimated continuously over annual periods. Key findings included the dominance of event loads by dissolved inorganic N and the strong positive correlation between discharge and particulate P concentrations. Quantification of hysteresis in relationships between nutrient concentrations and discharge provided information about the relative importance of near– versus far–channel sources during individual events. For example, elevated concentrations of dissolved inorganic N during recessing hydrograph limbs for the Puarenga Stream suggested diffuse delivery of N from an upstream source. Temporal inequality in estimated loading over a two–year period was high for TP as, for example, 50% of estimated cumulative two–year loads of TP were calculated to have been transported during 10–17% of the two–year time period. The effects of storm flow discharges on water quality in Lake Rotorua were studied at fine spatial and temporal resolution for a five–day period with high rainfall in summer. An intensive programme of lake and stream sampling was paired with application of a three–dimensional hydrodynamic–ecological model (ELCOM–CAEDYM) to specifically study how dynamic fluxes in water, sediment, N and P transport in the Ngongotaha Stream inflow influenced water quality and phytoplankton nutrient limitation in the transition zone present where the stream enters the lake. Wind–driven basin–scale horizontal circulations in the lake caused deflection of the inflowing stream which strongly influenced water quality in the littoral zone for a distance of up to 1 km from the stream mouth, thus highlighting the potential importance of basin–scale horizontal transport processes in mediating the effects of storm flow discharges on lake water quality. The nutrient limitation status of phytoplankton varied both spatially and temporally within the lake in relation to nutrient transport processes, emphasising the relatively fine spatial and temporal scales at which key processes that affect phytoplankton ecology can occur. Dilution of lake water by the stream inflow strongly affected the spatial distribution of chl a, although the highly spatially resolved sampling identified ‘hot spots’ within the nutrient–rich plume which contributed to fine scale (≈10–30 m) patchiness in the transition zone. The results of nutrient enrichment experiments indicated that such patchiness was consistent with a scenario of relative stimulation in the growth of lentic phytoplankton due to high nutrient availability in the spreading plume. To further examine the issue of nutrient bioavailability, chemical fractionation techniques and batch culture experiments were conducted to investigate spatial (between streams) and temporal (between periods of varying stream discharge) variations in the bioavailability of particulate P transported in storm flow for the two study streams. Bicarbonate–dithionate extraction indicated that 25–100% of particulate P transported in stream water samples collected during storm flow was potentially bioavailable if exposed to anoxia, e.g. in the lake hypolimnion during calm summer periods. Somewhat paradoxically though, bioassays indicated that, under oxic conditions in the laboratory, bioavailable P was actually higher in filtered samples (particulate P removed) than in unfiltered samples (higher TP concentrations, particulate P present). This result was attributed to net adsorption of dissolved inorganic P to the sediments present in the unfiltered treatments, and therefore highlights the importance of considering physicochemical characteristics of receiving environments when assessing bioavailability of P sorbed to sediments. Hence, by examining a range of spatial scales and integrating understanding gained using a range of research methods, this study has provided knowledge of underlying drivers of spatial and temporal variability in nutrient loading to lake ecosystems at scales ranging from global to a few metres. Furthermore, it has provided insight into how such variability can affect lake water quality. This knowledge can guide actions that are increasingly required to safeguard the services provided by lake ecosystems in a future with increasing global and local pressures on freshwaters

Nitrogen and phosphorus limitation of phytoplankton growth in New Zealand lakes: Implications for eutrophication control

We examine macronutrient limitation in New Zealand (NZ) lakes where, contrary to the phosphorus (P) only control paradigm, nitrogen (N) control is widely adopted to alleviate eutrophication. A review of published results of nutrient enrichment experiments showed that N more frequently limited lake productivity than P; however, stoichiometric analysis of a sample of 121 NZ lakes indicates that the majority (52.9%) of lakes have a mean ratio of total nitrogen (TN) to total phosphorus (TP) (by mass) indicative of potential P-limitation (>15:1), whereas only 14.0% of lakes have mean TN:TP indicative of potential N-limitation (<7:1). Comparison of TN, TP, and chlorophyll a data between 121 NZ lakes and 689 lakes in 15 European Union (EU) countries suggests that at the national scale, N has a greater role in determining lake productivity in NZ than in the EU. TN:TP is significantly lower in NZ lakes across all trophic states, a difference that is driven primarily by significantly lower in-lake TN concentrations at low trophic states and significantly higher TP concentrations at higher trophic states. The form of the TN:TP relationship differs between NZ and the EU countries, suggesting that lake nutrient sources and/or loss mechanisms differ between the two regions. Dual control of N and P should be the status quo for lacustrine eutrophication control in New Zealand and more effort is needed to reduce P inputs

Reducing the external environmental costs of pastoral farming in New Zealand: experiences from the Te Arawa lakes, Rotorua

Decades of nutrient pollution have caused water quality to decline in the nationally iconic Te Arawa (Rotorua) lakes in New Zealand. Pastoral agriculture is a major nutrient source, and therefore this degradation represents an external environmental cost to intensive farming. This cost is borne by the wider community, and a major publically funded remediation programme is now under way. This article describes the range of actions being taken to reduce nutrient loads from internal (lake bed sediments) and external (primarily diffuse) sources in the lake catchments. The high economic cost and uncertain efficacy of engineering-based actions to reduce internal nutrient loads is highlighted. Major changes to land management practices to control diffuse nutrient pollution are required throughout New Zealand if the need for costly and lengthy remediation programmes elsewhere is to be avoided. More action to educate farmers and the public about eutrophication issues, development and enforcement of environmental standards, and further consideration of the use of market-based instruments are proposed as ways to correct the current market failure

Reducing the external environmental costs of pastoral farming in New Zealand: experiences from the Te Arawa lakes, Rotorua

Decades of nutrient pollution have caused water quality to decline in the nationally iconic Te Arawa (Rotorua) lakes in New Zealand. Pastoral agriculture is a major nutrient source, and therefore this degradation represents an external environmental cost to intensive farming. This cost is borne by the wider community, and a major publically funded remediation programme is now under way. This article describes the range of actions being taken to reduce nutrient loads from internal (lake bed sediments) and external (primarily diffuse) sources in the lake catchments. The high economic cost and uncertain efficacy of engineering-based actions to reduce internal nutrient loads is highlighted. Major changes to land management practices to control diffuse nutrient pollution are required throughout New Zealand if the need for costly and lengthy remediation programmes elsewhere is to be avoided. More action to educate farmers and the public about eutrophication issues, development and enforcement of environmental standards, and further consideration of the use of market-based instruments are proposed as ways to correct the current market failure

Quantifying temporal and spatial variations in sediment, nitrogen and phosphorus transport in stream inflows to a large eutrophic lake

High-frequency sampling of two major stream inflows to a large eutrophic lake (Lake Rotorua, New Zealand) was conducted to measure inputs of total suspended sediment (TSS), and fractions of nitrogen and phosphorus (P). A total of 17 rain events were sampled, including three during which both streams were simultaneously monitored to quantify how concentration–discharge (Q) relationships varied between catchments during similar hydrological conditions. Dissolved inorganic nitrogen (DIN) concentrations declined slightly during events, reflecting dilution of groundwater inputs by rainfall, whereas dissolved inorganic P (PO₄–P) concentrations were variable and unrelated to Q, suggesting dynamic sorptive behaviour. Event loads of total nitrogen (TN) were predominantly DIN, which is available for immediate uptake by primary producers, whereas total phosphorus (TP) loads predominantly comprised particulate P (less labile). Positive correlations between Q and concentrations of TP (and to a lesser extent TN) reflected increased particulate nutrient concentrations at high flows. Consequently, load estimates based on hourly Q during storm events and concentrations of routine monthly samples (mostly base flow) under-estimated TN and TP loads by an average of 19% and 40% respectively. Hysteresis with Q was commonly observed and inclusion of hydrological variables that reflect Q history in regression models improved predictions of TN and TP concentrations. Lorenz curves describing the proportions of cumulative load versus cumulative time quantified temporal inequality in loading. In the two study streams, 50% of estimated two-year loads of TN, TP and TSS were transported in 202–207, 76–126 and 1–8 days respectively. This study quantifies how hydrological and landscape factors can interact to influence pollutant flux at the catchment scale and highlights the importance of including storm transfers in lake loading estimates

Relationships between land use and nitrogen and phosphorus in New Zealand lakes

Developing policies to address lake eutrophication requires an understanding of the relative contribution of different nutrient sources and of how lake and catchment characteristics interact to mediate the source–receptor pathway. We analysed total nitrogen (TN) and total phosphorus (TP) data for 101 New Zealand lakes and related these to land use and edaphic sources of phosphorus (P). We then analysed a sub-sample of lakes in agricultural catchments to investigate how lake and catchment variables influence the relationship between land use and in-lake nutrients. Following correction for the effect of co-variation amongst predictor variables, high producing grassland (intensive pasture) was the best predictor of TN and TP, accounting for 38.6% and 41.0% of variation, respectively. Exotic forestry and urban area accounted for a further 18.8% and 3.6% of variation in TP and TN, respectively. Soil P (representing naturally-occurring edaphic P) was negatively correlated with TP, owing to the confounding effect of pastoral land use. Lake and catchment morphology (zmax and lake : catchment area) and catchment connectivity (lake order) mediated the relationship between intensive pasture and in-lake nutrients. Mitigating eutrophication in New Zealand lakes requires action to reduce nutrient export from intensive pasture and quantifying P export from plantation forestry requires further consideration

Modelling water, sediment and nutrient fluxes from a mixed land-use catchment in New Zealand: effects of hydrologic conditions on SWAT model performance

The Soil Water Assessment Tool (SWAT) was configured for the Puarenga Stream catchment (77 km2), Rotorua, New Zealand. The catchment land use is mostly plantation forest, some of which is spray-irrigated with treated wastewater. A Sequential Uncertainty Fitting (SUFI-2) procedure was used to auto-calibrate unknown parameter values in the SWAT model which was applied to the Puarenga catchment. Discharge, sediment, and nutrient variables were then partitioned into two components (base flow and quick flow) based on hydrograph separation. A manual procedure (one-at a-time sensitivity analysis) was then used to quantify parameter sensitivity for the two hydrologically-separated regimes. Comparison of simulated daily mean discharge, sediment and nutrient concentrations with high-frequency, event-based measurements allowed the error in model predictions to be quantified. This comparison highlighted the potential for model error associated with quick-flow fluxes in flashy lower-order streams to be underestimated compared with low-frequency (e.g. monthly) measurements derived predominantly from base flow measurements. To overcome this problem we advocate the use of high-frequency, event-based monitoring data during calibration and dynamic parameter values with some dependence on discharge regime. This study has important implications for quantifying uncertainty in hydrological models, particularly for studies where model simulations are used to simulate responses of stream discharge and composition to changes in irrigation and land management

Inhibition of Ral GTPases Using a Stapled Peptide Approach

Aberrant Ras signalling drives numerous cancers and drugs to inhibit this are urgently required. This compelling clinical need, combined with recent innovations in drug discovery including the advent of biologic therapeutic agents, has propelled Ras back to the forefront of targeting efforts. Activated Ras has proved extremely difficult to target directly and the focus has moved to the main downstream Ras-signalling pathways. In particular, the Ras-Raf and Ras-PI3K pathways have provided conspicuous enzyme therapeutic targets, which were more accessible to conventional drug-discovery strategies. The Ras-RalGEF-Ral pathway is a more difficult challenge for traditional medicinal development and there have therefore been few inhibitors reported that disrupt this axis. We have used our structure of a Ral-effector complex as a basis for the design and characterization of α-helical stapled peptides that bind selectively to active, GTP-bound Ral proteins and that compete with downstream effector proteins. The peptides have been thoroughly characterized biophysically. Crucially, the lead peptide enters cells and is biologically active, inhibiting isoform-specific RalB-driven cellular processes. This therefore provides a starting point for therapeutic inhibition of the Ras-RalGEF-Ral pathway.This work was supported by a Cambridge Cancer Centre Pump Priming award to CA, DO and HRM, a BBSRC Studentship to NSC, and a National Institutes for Health grant (CA71443) and the Welch Foundation (grant number I-1414) to MAW.This is the final version of the article. It first appeared from the American Society for Biochemistry and Molecular Biology via https://doi.org/10.1074/jbc.M116.72024

Reference and current Trophic Level Index of New Zealand lakes: benchmarks to inform lake management and assessment

Knowledge of trophic status is fundamental to understanding the condition and function of lake ecosystems. We developed regression models to predict chlorophyll a concentrations (chl a) in New Zealand lakes for reference and current states, based on an existing dataset of total nitrogen (TN) and total phosphorus (TP) concentrations for 1031 lakes. Models were then developed to predict Secchi depth based on chl a and a sediment resuspension term applicable to shallow lakes. Estimates of all four Trophic Level Index (TLI) variables (chl a, TN, TP and Secchi depth) were analysed to estimate reference and current state TLI for the nationally representative sample of 1031 lakes. There was a trend of eutrophication between reference and current states, with systematic differences among lake geomorphic types. Mean chl a increased 3.5-fold (2.42 mg m­¯­­­³ vs. 8.32 mg m¯³) and mean Secchi depth decreased (indicating lower clarity) by approximately one-third (9.62 m vs. 6.48 m) between reference and current states. On average, TLI increased by 0.67, with the TLI increase >1 in approximately one-third (31%) of lakes. This study informs the status of lake ecosystems in NZ and provides benchmarks to guide management and assessment