Hydrological Stress Research Articles

Solute transport modelling for assessing the duration of river flow to improve the groundwater quality in an intensively irrigated deltaic region

Groundwater modelling is an important management tool to study the behaviour of aquifer system under various hydrological stresses. Present study was carried out in deltaic regions of the Cauvery river, with an objective of estimating the minimum river flow required to improve the groundwater quality by numerical modelling. Cauvery river delta is the most productive agricultural plains of south India, but the agricultural activities during the last few decades have decreased due to limited flow in the river and increasing concentration of solutes in groundwater in the eastern parts. In order to understand the causes for increasing concentration, a three-layered finite-difference flow model was formulated to simulate the groundwater head and solute transport. The model was used to simulate the groundwater flow and solute transport for 5 years from July 2007 to June 2012. There was a fairly good agreement between the computed and observed groundwater heads. The chloride and nitrate ions were considered for solute transport modelling. Observed and simulated temporal variation in chloride and nitrate concentrations were comparable. The simulated solute concentrations from July 2007 to June 2012 showed an accumulation of solutes in groundwater of coastal part of the study area. The model was used to find the flow to be maintained in the river and rainfall recharge required to flush the ions into the sea. This can be achieved by maintaining minimal flow in the river and through regulation of fertilizer use as well as by creating awareness of sustainable use of groundwater in this area.

Modelling the vulnerability of groundwater to contamination in an unconfined alluvial aquifer in Pakistan

The area of Thal Doab is located in the Indus Basin and is underlain by a thick alluvial aquifer called the Thal Doab aquifer (TDA). The TDA is undergone intense hydrological stress owing to rapid population growth and excessive groundwater use for livestock and irrigated agricultural land uses. The potential impact of these land uses on groundwater quality was assessed using a DRASTIC model in a Geographic Information System environment. Seven DRASTIC thematic maps were developed at fixed scale and then combined into a groundwater vulnerability map. The resultant vulnerability index values were grouped into four zones as low, moderate, high and very high. The study has established that 76% of the land area that is underlain by the TDA has a high to very high vulnerability to groundwater contamination mainly because of a thin soil profile, a shallow water table and the presence of soils and sediments with high hydraulic conductivity values. In addition, only 2 and 22% of the total area lie in low and moderate vulnerability zones, respectively. The outcomes of this study can be used to improve the sustainability of the groundwater resource through proper land-use management.

Fording differences? Conditions mitigating water insecurity in the Niger River Basin

River basins are an extremely important source of freshwater for Africa and the impact of climate change on these communities constitutes an important question worth studying. Among these basins, the Niger River Basin is an ideal candidate for meso-level theory testing of climate change-induced political violence because of its importance as one of the largest sources of freshwater in Africa, its high vulnerability to climate change, and its location in a politically unstable region. This paper utilizes the benefits of GIS to test whether effects of water insecurity on the various incidences of political violence are conditional on economic, geographic, and social means of connectivity. Our analysis uses the density of secondary road networks, the geographic distance to the Niger River, and a shared co-ethnicity with one's head-of-state to evaluate the impact of hydrological stress and its subsequent risk for political violence across nine West African countries from 1997 to 2012. Using climatological data and an econometric de-trending method, we measure the separate, substantive impact that individualized changes in precipitation trend and precipitation variability have for the incidence of ACLED's political violence events, conditional on local economic, geographic, and social factors. Our results reveal a complicated web of circumstances under which certain forms of political violence are more/less likely to be observed. The implications of this analysis serve as a call for a closer inspection of the micro-channels by which climate stress impacts heterogeneous communities in the developing world.

Spatial and temporal dynamics of macrophyte cover in a large regulated river

The River Ebro basin is extensively dammed. Dams alter the geomorphological functioning of the river by altering its flow regime (e.g. reducing mean and maximum discharges), increasing bed stability (armouring) and decreasing turbidity (water clarity). These effects, together with an increase in nutrient concentrations and water temperature, have generated optimal conditions for the proliferation of aquatic macrophytes. In this paper, we analyse the temporal and spatial changes of macrophyte cover in the lowermost Ebro through a series of field campaigns carried out between 2009 and 2010. Special attention was paid to the spatial distribution of macrophytes in relation to flow hydraulics, channel geometry and bed sedimentology. Temporal changes in macrophyte cover were analysed in relation to the frequency and magnitude of both natural floods and flushing flows (artificial flow releases from dams with generally a magnitude that equates around a2-year flood in the river). Spatially, the proportion of macrophytes along the reaches showed a variable pattern, with a succession of areas with both high and low plant density, coinciding with the alternation of riffles and pools in the channel. The highest values of plant cover (>65%) occurred in riffles and in transition to riffle areas, while the lowest densities (1% or almost negligible) were observed in pools and transition to pool areas. Water depth and the grain-size distribution of the riverbed materials (i.e. D84), are found to be the main factors controlling the degree of plant cover in the lower Ebro. Temporally, the macrophyte proportion varied during the hydrological year, with a clear increment from late spring to early autumn (i.e. vegetation cover reached 40%, on average, of the channel surface). Macrophyte coverage decreases immediately following a flushing flow but in the long term, vegetation re-occupied the area again, even slightly increasing in some sections; overall, the mean percentage of macrophyte cover was 19% higher at the end of the study period, despite the numerous flow events occurred on the meantime. This increase enhanced riverbed stability, which in turn reduced the possibility for bed-material entrainment. This study empirically confirms the necessity of improving the management options applied in the lower Ebro with complementary measures to help maximise the efficiency of flow releases (for instance, subject the macrophytes to a severe hydrological stress by decreasing discharge before a given flushing flow, undertake localise mechanical removal of plants in areas where density is high, and increase the frequency of floods in winter time when macrophyte stands are weaker).

Land degradation trend assessment over Iberia during 1982-2012

Land degradation is recognized as an important environmental and social problem in arid and semi-arid regions, particularly within a climate change context. In the last three decades the entire Mediterranean basin has been affected by more frequent droughts, covering large sectors and often lasting more than one year. The Iberian Peninsula has been equally affected by intense drought events since the 1980s. According to the latest IPCC report the Mediterranean region will suffer further hydrological stress in the coming decades, as a consequence of diminishing of precipitation and increasing of average and extreme temperatures. This climatic outlook coupled with the land abandonment and/or intensification of some areas requires a continuous monitoring and early detection of degradation. The present work intends to contribute to such objectives.Land degradation could be stated as a longstanding deterioration in ecosystems productivity. Here we assess the ability of NDVI to be used as an indicator of land degradation over Iberia, from 1982 to 2012. The negative trends of the residuals obtained after removing the precipitation influence on NDVI were assumed to indicate land degradation. A widespread land improvement was observed over Iberia with few hot spots of land degradation located mainly in central and southern sectors and in east Mediterranean and Atlantic coasts. The comparison of spatial patterns of residual trends with dryness for the aridity regions over Iberia highlighted the relatively small fraction of land degradation that experiences an increased dryness, although almost totality belonging to semi-arid region. On the other hand, land improvement is only associated with a tendency of wetness in the northeastern humid sector. Moreover, less than 20% of the area presenting land degradation corresponds to regions associated with land cover changes, being the new land cover types associated with transitional woodland-shrub, permanent and annual crops and permanently irrigated land areas.

Analytical and statistical approach for evaluating the effects of a river barrage on river–aquifer interactions

AbstractThe construction of a river barrage can increase groundwater levels upstream of the barrage during the rainy season. Analytical and statistical approaches were applied to evaluate the relationship between groundwater and river water at the Changnyeong–Haman river barrage in Korea using time series data of water level and electrical conductivity from June 2011 to September 2014. An artificial neural network based time series model was designed to filter out the effect of rainfall from the groundwater level data in the study area. Aquifer diffusivity and river resistance were estimated from the analytical solution of a one‐dimensional unit step response function by using the filtered groundwater level data. River resistance increased in response to groundwater level fluctuations. Cross‐correlation analyses between the groundwater and the river water showed that the lag time increased during the observation period for both the water level and the electrical conductivity while the cross‐correlation function declined for the same period. The results indicated that a constant river stage maintained at the river barrage can weaken the hydrologic stress and reduce the exchange of material between the river and the adjacent aquifer because of the deposition of fine sediment on the river bottom and walls. Copyright © 2016 John Wiley & Sons, Ltd.

Validation of a model with climatic and flow scenario analysis: case of Lake Burrumbeet in southeastern Australia.

Forecast evaluation is an important topic that addresses the development of reliable hydrological probabilistic forecasts, mainly through the use of climate uncertainties. Often, validation has no place in hydrology for most of the times, despite the parameters of a model are uncertain. Similarly, the structure of the model can be incorrectly chosen. A calibrated and verified dynamic hydrologic water balance spreadsheet model has been used to assess the effect of climate variability on Lake Burrumbeet, southeastern Australia. The lake level has been verified to lake level, lake volume, lake surface area, surface outflow and lake salinity. The current study aims to increase lake level confidence model prediction through historical validation for the year 2008-2013, under different climatic scenario. Based on the observed climatic condition (2008-2013), it fairly matches with a hybridization of scenarios, being the period interval (2008-2013), corresponds to both dry and wet climatic condition. Besides to the hydrologic stresses uncertainty, uncertainty in the calibrated model is among the major drawbacks involved in making scenario simulations. In line with this, the uncertainty in the calibrated model was tested using sensitivity analysis and showed that errors in the model can largely be attributed to erroneous estimates of evaporation and rainfall, and surface inflow to a lesser. The study demonstrates that several climatic scenarios should be analysed, with a combination of extreme climate, stream flow and climate change instead of one assumed climatic sequence, to improve climate variability prediction in the future. Performing such scenario analysis is a valid exercise to comprehend the uncertainty with the model structure and hydrology, in a meaningful way, without missing those, even considered as less probable, ultimately turned to be crucial for decision making and will definitely increase the confidence of model prediction for management of the water resources.

Sensitivity of river fishes to climate change: The role of hydrological stressors on habitat range shifts

Climate change will predictably change hydrological patterns and processes at the catchment scale, with impacts on habitat conditions for fish. The main goal of this study is to assess how shifts in fish habitat favourability under climate change scenarios are affected by hydrological stressors. The interplay between climate and hydrological stressors has important implications in river management under climate change because management actions to control hydrological parameters are more feasible than controlling climate. This study was carried out in the Tamega catchment of the Douro basin. A set of hydrological stressor variables were generated through a process-based modelling based on current climate data (2008–2014) and also considering a high-end future climate change scenario. The resulting parameters, along with climatic and site-descriptor variables were used as explanatory variables in empirical habitat models for nine fish species using boosted regression trees. Models were calibrated for the whole Douro basin using 254 fish sampling sites and predictions under future climate change scenarios were made for the Tamega catchment. Results show that models using climatic variables but not hydrological stressors produce more stringent predictions of future favourability, predicting more distribution contractions or stronger range shifts. The use of hydrological stressors strongly influences projections of habitat favourability shifts; the integration of these stressors in the models thinned shifts in range due to climate change. Hydrological stressors were retained in the models for most species and had a high importance, demonstrating that it is important to integrate hydrology in studies of impacts of climate change on freshwater fishes. This is a relevant result because it means that management actions to control hydrological parameters in rivers will have an impact on the effects of climate change and may potentially be helpful to mitigate its negative effects on fish populations and assemblages.

Towards a more precisely defined macrophyte-dominated regime: the recent history of a shallow lake in Eastern Poland

Archived data and sedimentary macrofossil records of vegetation and invertebrates deposited in a 60-cm long sediment core were analysed to examine if macrophyte dominance was a permanent feature of the recent history of lowland Lake Kleszczow. For the last several centuries, the lake has not been dominated by phytoplankton but by floating-leaved vegetation at strongly reduced water level. Starting from the mid-nineteenth century, probably as a result of climate fluctuations, vegetation switched at first into submerged angiosperms, and then, in the second half of twentieth century, towards charophytes. Within charophytes there were switches between Chara globularis and C. vulgaris communities, depending on lake productivity or hydrological stress. No symptoms were detected of a switch to a turbid regime as a result of potential internal supply of phosphorus from sediments covered with a dense carpet of charophytes. Our study shows that within a longer period with clear water, the community of macro-vegetation can be highly dynamic. It can be represented by various types of vegetation as a response to different productivity levels and/or hydrological stress, largely determining the composition of other hydrobionts and course of various processes, and as a consequence, the functioning of the ecosystem and its resilience.

Methodological Proposal for Redesigning Informal Communities - Constructing Resilience in Hydrological Stress Conditions

Abstract The paper presents a methodological proposal in the form of a framework for redesigning informal settlements based on Low-impact Design and Development methodology. It involves the management of rainwater through the implementation of urban infrastructure on local scale in a decentralized and collaborative manner. It served as an object of study the region of Baixada de Jacarepagua, a vector of expansion of the city of Rio de Janeiro. The proposed framework adopts Action-Research methodology. The stages envisaged in the framework are: (i) initial, which involves approaching the community, establishing bonds and setting up a management group, (ii) diagnosis, and (iii) project. The application of the framework is demonstrated by means of a case study of the community, which typifies the slums in areas of marshland and the peripheral urban landscape. It is believed that this framework can guide the urban redesign of other communities within the perspective of sustainable development.

Physiological responses to extreme hydrological events in the Pantanal wetland: heterogeneity of a plant community containing super‐dominant species

AbstractAimsWe tested two mechanisms of adaptation to extreme hydrological stresses (flooding and drought) of species making up a tropical wetland plant community by measuring leaf gas exchange and water potential. We hypothesized that anoxic conditions that occur during flooding will decrease leaf gas exchange when compared to the dry season, and that ‘super‐dominant’ species will have a distinctive physiological advantage when compared to other plants within the community.LocationNorthern Pantanal wetland, Private Natural Heritage Reserve of the Brazilian Social Service of Commerce (RPPN‐SESC Pantanal), Mato Grosso, Brazil.MethodsTwo periods representing typical extreme hydrological conditions in the Pantanal wetland were selected based on historical soil and meteorological measurements: (1) a drought period when plants experience stress due to soil moisture deficits during a dry season that persists for several months (May to Sept), and (2) a flooding period when oxidation‐reduction potential is negative for 30 d or more (Mar or Apr), indicating anoxic stress. Measurements of gas exchange and leaf water potential were made on seven species in drought and flood stress conditions. The seven species represent the majority of the plant community.ResultsAs a whole, the plant community showed significantly lower potential net photosynthesis (PN) during flooding when soil oxidation‐reduction potential reached close to −900 mV when compared to the dry season, but the magnitude of the decline in PN was species specific. Not all super‐dominant species showed higher PN compared to non‐dominant species, but they did demonstrate higher stomatal conductance and transpiration leading to lower water use efficiency. The combination of higher PN despite low soil water content suggests that the plant community had access to deep water resources. This access was also confirmed by the midday leaf water potential, which was similar for the flood and dry seasons.ConclusionsResults suggest that the plant community may have high physiological performance under a wide range of soil oxidation‐reduction potentials. Higher PN rates of super‐dominant species indicate a physiological advantage of these species in the different hydrological conditions.

Island morphology, reef resources, and development paths in the Maldives

Maldivian paths for economic development have historically been constrained by the morphology of atoll islands and the availability of material resources. These constraints are most evident when examining the development of Male’, the Maldives’ capital and most populous island. Before the 1970s, Male’ was a rather typical atoll island, consisting of accumulated rubble and sand with an underlying lagoonal reef (faro) structure. Rising population and standard-of-living expectations in Male’ led to accelerated coral mining of Male’s reefs in the 1970s and 80s for both landfill and construction material, extending the island’s land surface across Male’s lagoon and reef flats, close to the edge of its underlying faro. This combination of mining and fill degraded the island’s natural defenses against wave events, resulting in disastrous floods in April 1987 and the fortification of the coastline with seawalls shortly thereafter. The degree of degradation to natural defenses and amount of investment in urban building stock have jointly locked Male’ into a “hard path” for coastal resilience engineering, and both the damage patterns and response to the 2004 Indian Ocean tsunami demonstrate that the Male’ model of development and degradation has spread to smaller Maldivian islands. While hard measures have proven successful in preventing further damage, their expense has led to greater interest in “soft path,” ecosystem-based resilience measures. The degree of local ecosystem damage, combined with high vulnerability to climate change and Male’s continued growth, means that such measures can only be seen as supplements to heavier fortification in the future, including raised (Th. Vilufushi) or artificial islands (Hulhumale’). The intersecting role hydrological stress on Maldivian groundwater has played in Male’s development path is also discussed.

Hierarchical modeling of a groundwater remediation capture system

Summary In this paper, we present a real-world demonstration of a generalized hierarchical approach for modeling complex groundwater systems, the hierarchical patch dynamics paradigm (HPDP). In particular, we illustrate how the HPDP approach enables flexible and efficient simulation of a complex contaminant capture system at one of the largest groundwater pump-and-treat remediation operations in Michigan. The groundwater flow system at the site exhibits a multi-scale pattern that is difficult to simulate using standard modeling tools because of the complex interaction between ambient hydrologic stresses and on-site remediation operations. The hierarchical modeling system was calibrated to water level measurements collected from 208 monitoring wells located both on-site and in its immediate proximity and flux measurements from 6 trenches on-site. Systematic hierarchical simulations, including forward and reverse particle tracking as well as integrated water budget analyses, were performed to study the on-going remediation. The hierarchical modeling results show that some contamination leaked off-site because of small-scale inefficiencies in the design of the remediation system. Thus, the HPDP approach provides an opportunity to analyze complex hydrological field environments in a pragmatic, time-efficient manner.

Replacing natural wetlands with stormwater management facilities: Biophysical and perceived social values

Urban expansion replaces wetlands of natural origin with artificial stormwater management facilities. The literature suggests that efforts to mimic natural wetlands in the design of stormwater facilities can expand the provision of ecosystem services. Policy developments seek to capitalize on these improvements, encouraging developers to build stormwater wetlands in place of stormwater ponds; however, few have compared the biophysical values and social perceptions of these created wetlands to those of the natural wetlands they are replacing. We compared four types of wetlands: natural references sites, natural wetlands impacted by agriculture, created stormwater wetlands, and created stormwater ponds. We anticipated that they would exhibit a gradient in biodiversity, ecological integrity, chemical and hydrologic stress. We further anticipated that perceived values would mirror measured biophysical values. We found higher biophysical values associated with wetlands of natural origin (both reference and agriculturally impacted). The biophysical values of stormwater wetlands and stormwater ponds were lower and indistinguishable from one another. The perceived wetland values assessed by the public differed from the observed biophysical values. This has important policy implications, as the public are not likely to perceive the loss of values associated with the replacement of natural wetlands with created stormwater management facilities. We conclude that 1) agriculturally impacted wetlands provide biophysical values equivalent to those of natural wetlands, meaning that land use alone is not a great predictor of wetland value; 2) stormwater wetlands are not a substantive improvement over stormwater ponds, relative to wetlands of natural origin; 3) stormwater wetlands are poor mimics of natural wetlands, likely due to fundamental distinctions in terms of basin morphology, temporal variation in hydrology, ground water connectivity, and landscape position; 4) these drivers are relatively fixed, thus, once constructed, it may not be possible to modify them to improve provision of biophysical values; 5) these fixed drivers are not well perceived by the public and thus public perception may not capture the true value of natural wetlands, including those impacted by agriculture.

Numerical Simulation and Prediction of Groundwater Flow in a Coastal Aquifer of Southern India

Chennai is one of the most water-stressed cities in south India due to rapid industrialization and urbanization. The well fields located in north and south of the Chennai city meets part of the city’s water requirement. The south Chennai aquifer is surrounded by saline surface water on all sides. Since 1990, the influence of seawater in to this freshwater aquifer has been reported as an issue for consideration and mitigation measures. Therefore, in the present study an attempt is made to comprehend the status of aquifer with present level of pumping/recharge and to predict the behavior with different hydrologic stresses. Numerical modeling was carried out by finite element approach using FEFLOW software. The model has been developed with three subsurface layers and simulation was processed from January 1998 to December 2020. The groundwater usage had varied from 11.3 MLD to 17.2 MLD during the period of study. If the recharge and discharge continue in a similar pattern, the maximum level of freshwater decline will be 0.32 m at the end of 2020. Hence, prediction of behavior of this aquifer for increased discharge and decreased recharge scenario has been carried out. It is found that with an increase of discharge, there is a sharp change in interface of seawater and freshwater. This model can be used as a tool to understand the aquifer regionally and to plan proper groundwater management measures.

굴포천 임시방수로 굴착구간 주변의 지하수 수위 변동 유형 분류

Characteristics of water-level changes in the Temporary Gulpocheon Discharge Channel were identified by observing and analyzing changes in the subterranean water level induced by hydrological stresses the underground aquifer. The subterranean water level refers to the level at which the pressure of subterranean water passing through the corresponding position has an equipotential value that is in equilibrium with the atmospheric pressure at that location. This water level is not fixed but changes in response to hydrological stress. It can be identified by repeatedly measuring the distance from the observation point to the surface of the subterranean water. The subterranean water-level change equation and the variance range of the hydrological curve of subterranean water over 24 hours at the Gimpo-Gimpo National Groundwater Monitoring Network (NGMN) were used as assessment factors. The variance characteristics of the subterranean water at the 18 monitoring system locations were classified into three impact, observational wish, and non-impact. The impact type accounted for 50% of the subterranean water of and accurately reflected the water-level changes due to hydrological stress, showing that distance is the major controlling factor. The observational wish type accounted for 27.8% of the subterranean water, and one of the two assessment factors did not meet the assessment factors. The nonimpact type accounted for 22.2% of the subterranean water. This type satisfied the two assessment factors and represents subterranean water-level changes response to precipitation.

Assessing the Effects of Periodic Flooding on the Population Structure and Recruitment Rates of Riparian Tree Forests

Riparian forest stands are subjected to a variety of hydrological stresses as a result of annual fluctuations in water levels during the growing season. Spring floods create additional water-related stress as a result of a major inflow of water that floods riverside land. This exploratory study assesses the impacts of successive floods on tree dynamics and regeneration in an active sedimentation area, while determining the age of the stands using the recruitment rates, tree structure and tree rings based on dendrochronological analysis. Environmental data were also recorded for each vegetation quadrat. In total, 2633 tree stems were tallied throughout the quadrats (200 m2), and tree specimens were analyzed based on the various flood zones. A total of 720 specimens were counted (100 m2 strip) to measure natural regeneration. Higher recruitment rates are noted for the no-flood zones and lower rates in active floodplains. During the period of the establishment of tree species, the survival rates are comparable between the flood zones and the no-flood zones. Tree diameter distribution reveals a strong predominance of young trees in flooded areas. Different factors appear to come into play in the dynamics of riparian forest stands, including the disruptions associated with successive flooding.

Hydrosedimentologic disturbance index applied to watersheds of Minas Gerais state

Ecological indicators have become important tools for assessment and monitoring of natural resources, being the understanding of the relationship between antropic activities and the environmental response essential for their structuring. Although the development of potential indicators may prove sensitive to many variables, they must demonstrate their ability to take the surrounding conditions, from those relatively preserved to those highly disturbed. Based on this premise, the development of the Hydrossedimentological DisturbanceIndex (HSDI) for environmental assessment at watersheds in Minas Gerais state, emerges as a potential tool to support decisions which should be focused on the improvement of natural resources management. A HSDI proposal was developed from the hydrological, climate and water quality database available in Minas Gerais state, highlighting sediment transport (ST), hydrological stress (HS), groundwater recharge (Rec) and current soil erosion potential (SEP), working with a robust tool for determining the weights of factors with appropriate scientific background and subsequent development of map for analyzing its distribution, having Paraopeba river watershed as study case.

Análisis de periodos secos en la cuenca Mediterránea en clima presente y condiciones de cambio climático a partir de modelos regionales de clima del proyecto ENSEMBLES

The hydrological stresses and specially the dry spells are one of the main climatic features of the Mediterranean regions and it can affect and lead to relevant impacts on ecosystems, agriculture and population. It is proposed the analysis of the annual mean dry spells length (DSML) from a group of Regional Climate Model (RCM) simulations of 25km horizontal resolution from ENSEMBLES European project. The capability of these RCMs to reproduce the DSML compared with ECAv6 gridded observational database is first studied in the baseline period (1961-2000). Then percentage change of the DSML from these RCMs forced by different Global Climate Models (GCMs) for future conditions (2021-2050) under A1B emission scenario respect to historical (1951-1980) climate conditions is evaluated. The results show the success of RCMs to reproduce the overall observed dry spells characteristics. A North-to-South gradient of DSML index along the Mediterranean basin is obtained in the baseline and historical periods, with the maximum length values located over Sahara desert and minimum over the mountain ranges on the northern part of the basin. High values also can be observed in the southern half of the Iberian Peninsula, western and southern coast of the Mediterranean Sea. The climate change analysis indicates a common increase of the DSML over the Mediterranean basin for all the GCM-forced RCM simulations.

Wood decay rates and macroinvertebrate community structure along contrasting human pressure gradients (Waikato, New Zealand)

Mass loss rates of wooden sticks (Betula platyphylla Sukaczev) and macroinvertebrate community composition were measured in the Waikato Region of northern New Zealand at 53 running water sites draining native forest catchments (reference), or characterised by urban, industrial, agroforestry or hydrological stressors. Overall wood substrates retained 80% of initial dry mass over 2–3 month incubation periods, equating to average daily decay coefficients (kd) of 0.0027 or 0.0002 when adjusted for degree days (kdd). There were no statistically significant differences in decay rates between stressor types and native forest reference sites. In contrast, macroinvertebrate richness and compositional metrics varied significantly from reference conditions for several stressor types. Wood decay rates were weakly related to macroinvertebrate community composition, while kdd was weakly but significantly related to % ‘worms’, %EPT* abundance and Quantitative Macroinvertebrate Community Index. The results indicate weak correspondence between macroinvertebrate indicators and wood decay rates, with spatial and temporal factors potentially masking stressor responses. Before wood decay can be widely used as an indicator of lotic ecosystem health there needs to be an improved understanding of environmental factors affecting breakdown rates.