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News Article | November 28, 2016
Site: www.eurekalert.org

Wouldn't it be great if we could tell the state of an ecosystem or the like - whether it's healthy or heading for a crisis - by keeping track of just a few key signals? Thanks to the theory of 'tipping points', that's not unthinkable. Now a team of researchers led by Alena Gsell of the Netherlands Institute of Ecology (NIOO-KNAW) has tested early warning signals: in lakes. In the Early Edition of PNAS online, they conclude that predicting works but not in all cases yet. The term 'tipping point' has become popular to describe sudden and fundamental changes that take place even though exterior conditions haven't changed as radically. Think of a financial crisis. Think of a wall that will fall down - like the Berlin Wall - or one that will end up being built somewhere else just as suddenly. And what's true for human society is also true for ecosystems: in shallow lakes, clear, limpid water may suddenly turn into smelly green soup. Once such a 'regime shift' has occurred, it's difficult or even impossible to get things back to the way they were. But that doesn't mean there are no alarm signals. There is in fact a whole range of statistical indicators that have been proposed as possible early warnings. An international team led by NIOO-researcher Alena Gsell - formerly of the Leibniz Institute of Freshwater Ecology and Inland Fisheries in Berlin - has now for the first time tested the potential of four of these indicators to be applied to a wide range of lakes. "We've looked at five lakes for which long-term monitoring data (16-34 years) is available", explains Alena Gsell. One of them is the Veluwemeer in the Netherlands, another Lake Washington in the United States. The good news is that in some cases, early-warning indicators were indeed detected up to several years ahead of the moment when a 'regime shift' would take place. "That leaves some time for water managers to step in and take appropriate measures." These indicators show that the resilience of lake ecosystems becomes less ahead of a regime shift. "It's something you can observe if you know an ecosystem well", says Gsell. Perturbations become bigger: water turns turbid temporarily, smaller zooplankton species are favoured and edible green algae lose ground to the less tasty bluegreens. But on the whole, the team's tests produced many negative results as well. According to Gsell, this mixed outcome shows that the early warning indicators do hold promise as a method, but are not yet as suitable for general application as had been hoped by many. For the early alarm signals to be more effective, argue the researchers, collecting long term data - an essential "window into the past" - isn't the only thing that's important. The methods for mining the data also need to become more advanced. More frequent data collection would help: per day or even hour, instead of per week or less. "If you look at the current state of the environment, investing in the adaptation of indicator methods would definitely be an effort well spent." The NIOO counts more than 300 staff members and students and is one of the largest research institutes of the Royal Netherlands Academy of Arts and Sciences (KNAW). The institute specialises in water and land ecology. Since 2011, the institute is located in an innovative and sustainable research building located in Wageningen, the Netherlands. The institute has an impressive research history stretching back 60 years and which spans the entire country and beyond its borders. Article: Evaluating early-warning indicators of critical transitions in natural aquatic ecosystems, Alena Sonia Gsell, Ulrike Scharfenberger, Deniz Özkundakci, Annika Walters, Lars-Anders Hansson, Annette B. G. Janssen, Peeter Nõges, Philip C. Reid, Daniel E. Schindler, Ellen van Donk, Vasilis Dakos & Rita Adrian, Proceedings of the National Academy of Sciences (PNAS), 23 november 2016 (Early Edition, alvast online voorafgaand aan officiële uitgave in tijdschrift), http://www. Institutions involved: Leibniz Institute of Freshwater Ecology and Inland Fisheries (Duitsland); Nederlands Instituut voor Ecologie (NIOO-KNAW); Free University of Berlin (Duitsland); Waikato Regional Council (Nieuw Zeeland); US Geological Survey (VS); Lund University (Zweden); Wageningen University; Estonian University of Life Sciences (Estland); Sir Alister Hardy Foundation for Ocean Science (VK); Plymouth University (VK); Marine Biological Association of the United Kingdom (VK); University of Washington (VS); ETH Zürich (Zwitserland)


Pronger J.,University of Waikato | Schipper L.A.,University of Waikato | Hill R.B.,Waikato Regional Council | Campbell D.I.,University of Waikato | McLeod M.,Landcare Research
Journal of Environmental Quality | Year: 2014

The drainage and conversion of peatlands to productive agroecosystems leads to ongoing surface subsidence because of densification (shrinkage and consolidation) and oxidation of the peat substrate. Knowing the rate of this surface subsidence is important for future land-use planning, carbon accounting, and economic analysis of drainage and pumping costs. We measured subsidence rates over the past decade at 119 sites across three large, agriculturally managed peatlands in the Waikato region, New Zealand. The average contemporary (2000s-2012) subsidence rate for Waikato peatlands was 19 ± 2 mm yr-1 (± SE) and was significantly less (p = 0.01) than the historic rate of 26 ± 1 mm yr-1 between the 1920s and 2000s. A reduction in the rate of subsidence through time was attributed to the transition from rapid initial consolidation and shrinkage to slower, longterm, ongoing oxidation. These subsidence rates agree well with a literature synthesis of temperate zone subsidence rates reported for similar lengths of time since drainage. A strong nonlinear relationship was found between temperate zone subsidence rates and time since initial peatland drainage: Subsidence (mm yr-1) = 226 × (years since drained)-0.59 (R2 = 0.88). This relationship suggests that time since drainage exerts strong control over the rate of peatland subsidence and that ongoing peatland subsidence rates can be predicted to gradually decline with time in the absence of major land disturbance. © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America.


Collier K.J.,Waikato Regional Council | Collier K.J.,University of Waikato | Hamer M.P.,Waikato Regional Council
Freshwater Biology | Year: 2013

Contemporary patterns of land development mean that suitable reference sites for low-gradient stream and non-wadeable river biomonitoring are difficult to locate, requiring alternative approaches for benchmarking human impacts. We use two strongly harmonised macroinvertebrate data sets for wadeable streams (180 sites) and non-wadeable rivers (30 sites) to (i) quantify metric response differentials across a regional landcover pressure gradient in northern New Zealand; (ii) interpolate reference condition for waterway types lacking comparable reference sites and (iii) inform development of narrative condition bands for data-poor waterway types. Cumulative distribution functions of per cent waterway length indicated that near-shore littoral samples from non-wadeable rivers had fewer total and EPT (Ephemeroptera, Plecoptera and Trichoptera) taxa than wadeable streams, which had higher % EPT abundance and lower % Crustacea abundance. Community composition differed significantly among non-wadeable river and wadeable hard-bottom and soft-bottom stream samples, reflecting factors associated with catchment altitude, slope, rainfall and landuse intensity. Ephemeroptera, Plecoptera and Trichoptera richness was the only metric evaluated that significantly reflected landcover across all waterway types. The intercept of the 60th percentile quantile regression line at 100% native vegetation cover provided the best approximation of median EPT taxa richness in an independent reference site data set for hard-bottom streams. Applying the same interpolation to samples from soft-bottom streams and non-wadable rivers that lacked regional reference sites indicated median reference expectations of 9 and 11 EPT taxa, respectively, and a consistent differential across the pressure gradient relative to hard-bottom streams of seven taxa and five taxa, respectively. The derived response differentials enabled the development of narrative bands for directly comparing ecological condition of data-poor stream and river types. Quantification of ecological response differentials can provide an alternative means of benchmarking macroinvertebrate metrics in the absence of suitable reference sites. © 2013 John Wiley & Sons Ltd.


Vant B.,Waikato Regional Council
New Zealand Journal of Forestry | Year: 2013

The Council has operated a water-quality monitoring program at Lake Taupo since 1994. A deep water site near the middle of the lake is visited every two to four weeks, and water samples are collected and field measurements made. The graphs show the monthly changes in water quality between 1995 and 2011. Much of the rain falling on the Taupo catchment area of 2,800 square kilometers percolates through the soil and is stored underground as ground water, in some cases for many years, before finally entering the streams and then the lake. The groundwater therefore contains some of the nitrogen leached from historic land use practices but which has not yet entered the lake. When the variation to the plan was developed it was anticipated that, despite capping, the loads of nitrogen entering the lake in its inflows would continue to increase until the offsetting began to take effect. It was expected that it would take several decades or more before the full effects of intervention would be seen in the lake.


Barnett A.L.,University of Waikato | Schipper L.A.,University of Waikato | Taylor A.,Waikato Regional Council | Balks M.R.,University of Waikato | Mudge P.L.,Landcare Research
Agriculture, Ecosystems and Environment | Year: 2014

A previous temporal sampling study of New Zealand soils under different grazing systems indicated that soils on flat land under dairy farming had lost significant amounts of C and N in the last few decades, while soils under drystock farming on flat land had not. This result suggested that dairy farms would have lower soil C stocks than adjacent drystock farms. To test this hypothesis, we sampled 25 adjacent dairy and drystock farms to 0.6m depth and analysed samples for C, N and soil dry bulk density by horizon. Paired sampling sites were on average 108m apart, on the same soil with similar slope, aspect and topography and had been in that farming system for at least 10 years prior. The average stocking rate for dairy farms (24 stock units ha-1) was higher (P<0.01) than drystock farms (14 stock units ha-1). The mean total C and total N stocks for the whole soil profile (0-0.6m) were 173tCha-1 and 15.7tNha-1 for the dairy farms and 183tCha-1 and 16.1tNha-1 for the drystock farms and these were not significantly different. However, when the soil horizons were considered separately, the A horizon of dairy farms had significantly lower C (8tCha-1, P<0.05) than drystock farms. The A horizon thickness under dairy farming was also shallower (P<0.05) with a greater soil dry bulk density (P<0.05) than the drystock farms indicating soil compaction, presumably due to higher stocking rates and heavier animals on dairy farms. Changes in soil dry bulk density and A horizon depth offset one another and the total mass of soil sampled from the A horizons was the same (0.14±0.01tm-2). Therefore, the significant difference in soil C of the A horizon was likely to be a consequence of land management rather than as a result of sampling different masses of soil. Lower soil C content of the A horizon in this paired site study is consistent with an earlier sampling using temporal comparisons. We do not know the causes for these differences in C, but they might be linked to the higher stocking rates of dairy systems, where large dairy cows exert greater physical pressure on the soil, consume more above ground biomass, and deposit more intense urine patches that have been linked to solubilisation of soil C. © 2013 Elsevier B.V.


David B.O.,Waikato Regional Council | Hamer M.P.,Waikato Regional Council
Marine and Freshwater Research | Year: 2012

Worldwide, human-mediated disruption of river networks by artificial structures negatively affects migratory fish species. To creatively solve part of this problem, we assessed the effectiveness of mussel spat ropes for improving fish passage past perched culvert structures. We used a beforeaftercontroltreatment design to test our hypothesis that relative abundances of 'young-of-the-year' migratory fish species would increase following rope installation in a New Zealand stream. Results following remediation indicated a significant three- to four-fold increase in fish abundance relative to a control stream. Although four species (banded kokopu (Galaxias fasciatus), redfin bullies (Gobiomorphus huttoni), longfin eels (Anguilla dieffenbachii) and shortfin eels (Anguilla australis)) were present at both the treatment and control stream sites, the increased fish relative abundance at the treatment site was driven primarily by an increase in 'young-of-the-year' banded kokopu. The present study has shown that mussel spat ropes can significantly improve fish relative abundances above severely perched culverts, but may not be effective for all species present. Future use of ropes for evaluating passage efficacy for other species, and for a wider range of barrier situations globally, may greatly extend the application of this cost-effective tool. © 2012 CSIRO.


Taylor M.D.,Waikato Regional Council | Kim N.D.,Waikato Regional Council | Hill R.B.,Waikato Regional Council | Chapman R.,Soil and Land Evaluation Ltd
Soil Use and Management | Year: 2010

An ongoing programme of soil quality assessment in the Waikato region of New Zealand is providing baseline data and allowing identification of the impacts of land use and associated key soil quality issues. In this paper, we review the strengths and weaknesses of key soil quality indicators and provide summary statistics for chemical, physical and biochemical parameters in both background and production soils of the Waikato Region. Statistical comparison of production to background soils, time related trends, relative surface enrichments, and correlations enable us to infer likely and potential impacts of human activity on the region's soil resource. Five key issues that cause loss of soil resource have been identified. These are soil compaction, loss of soil organic matter, excessively high fertility levels, erosion risk, and accumulation of contaminants. In addition, evidence exists for accelerated attack or weathering of aluminosilicate minerals in farmed soils [dealumination, Australian Journal Soil Research (2009) vol. 47, 828-838], a process previously only recognized in soils adjacent to aluminium smelters. © 2010 The Authors. Journal compilation © 2010 British Society of Soil Science.


Wilding T.K.,Colorado State University | Brown E.,Waikato Regional Council | Collier K.J.,University of Waikato
Environmental Monitoring and Assessment | Year: 2012

Tidal streams are ecologically important components of lotic network, and we identify dissolved oxygen (DO) depletion as a potentially important stressor in freshwater tidal streams of northern New Zealand. Other studies have examined temporal DO variability within rivers and we build on this by examining variability between streams as a basis for regional-scale predictors of risk for DO stress. Diel DO variability in these streams was driven by: (1) photosynthesis by aquatic plants and community respiration which produced DO maxima in the afternoon and minima early morning (range, 0.6-4.7 g/m 3) as a product of the solar cycle and (2) tidal variability as a product of the lunar cycle, including saline intrusions with variable DO concentrations plus a small residual effect on freshwater DO for low-velocity streams. The lowest DO concentrations were observed during March (early autumn) when water temperatures and macrophyte biomass were high. Spatial comparisons indicated that lowgradient tidal streams were at greater risk of DO depletions harmful to aquatic life. Tidal influence was stronger in low-gradient streams, which typically drain more developed catchments, have lower reaeration potential and offer conditions more suitable for aquatic plant proliferation. Combined, these characteristics supported a simple method based on the extent of low-gradient channel for identifying coastal streams at risk of DO depletion. High-risk streams can then be targeted for riparian planting, nutrient limits and water allocation controls to reduce potential ecological stress. © Springer Science+Business Media B.V. 2012.


Collier K.J.,Waikato Regional Council | Collier K.J.,University of Waikato | Olsen A.R.,U.S. Environmental Protection Agency
Marine and Freshwater Research | Year: 2013

We investigated outcomes of three monitoring networks for assessing ecological character and condition of wadeable streams, Waikato region, New Zealand. Site selection was based on professional judgment, stratification within categories of watershed characteristics, or on using an unequal-probability survey design. The professional-judgment network, stratified network and all site analyses included more ≥4th-order streams than for the probability-network survey-design estimates Professional-judgment and stratified network sites and survey-design analyses incorporated higher-quality catchments with coarser substrates. Cumulative frequency distributions indicated that the stratified and/or judgmental networks yielded fewer taxa than did the probability network, and that the stratified network provided lower estimates of the macroinvertebrate community index (MCI). Compared with the probability-network survey-design analysis, the stratified network site analysis underestimated percentage stream length classed as 'Excellent' by the quantitative MCI, and the professional-judgment site and survey-design analyses overestimated the percentage classed 'Fair' by the average score per metric. We conclude that deriving reliable estimates of wadeable stream character and condition requires (1) clearly defining and quantifying the target population for which inferences will be drawn, (2) accounting for probability of site selection and (3) optimising spatial representation across dominant stressor gradients. © 2013 CSIRO.


Woodward S.J.R.,Lincoln Agritech Ltd. | Stenger R.,Lincoln Agritech Ltd. | Hill R.B.,Waikato Regional Council
Transactions of the ASABE | Year: 2016

While analysis of river water quality time series data alone allows observation of means, variances, trends, and seasonality, it cannot elucidate the catchment mechanisms responsible for these observations. Incorporating river flow data into the analysis allows additional insight to be gained into the mechanisms driving water quality change. Twenty-year series of monthly water quality samples were analyzed alongside high-resolution flow records in 26 catchments across the agriculturally dominated Waikato region of New Zealand. Concentration-discharge relationships indicated the importance of near-surface flow paths in transporting nitrogen and non-dissolved phosphorus species from the land into rivers. Dissolved phosphorus, on the other hand, appears to be discharged primarily in deeper groundwater carrying higher concentrations of geogenic origin. Subsequent data stratification was able to explain the origin of nitrate or phosphorus trends in some catchments as being due to either historical or recent land use changes. These results highlight the value of combined analysis of water quality data with river flow records. © 2016 American Society of Agricultural and Biological Engineers.

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