Long-term Monitoring Network Research Articles

The disappearing Antilles Current dominates the weakening meridional heat transport in the North Atlantic Ocean under global warming

The Antilles Current (AC) off the Bahamas Islands is an important component for both wind-driven and thermohaline circulation system in the North Atlantic. The evolution of AC intensity could exert substantial impacts on mid-latitude climate and surrounding environment. For instance, an anomalous weaker AC is found to decelerate the nutrient transport in the shelf regions, risking the deep-water corals. In addition, a weaker AC could reduce the poleward heat transport of the Gulf Stream and the North Atlantic Drift and further influence the climate in Western Europe. Based on nine high-resolution coupled climate models, we find a 3.8 Sv weakening of the AC, which is equivalent to 63% of its climatology transport during 1950–2050. The deceleration of AC introduces a −0.17 PW of heat transport decrement, dominating the total heat transport change across 26.5° N. Further analysis reveals that change of AC is mainly attributed to the evolution of thermohaline circulation in a changing climate and is partly influenced by wind stress curl in the North Atlantic. Our finding highlights the needs to establish a long-term monitoring network for the AC and a comprehensive understanding of associated impacts.

Observations reveal onshore acceleration and offshore deceleration of the Kuroshio Current in the East China Sea over the past three decades

The Kuroshio Current (KC) in the East China Sea is one of the most prominent components of the ocean circulation system in the North Pacific. The onshore intensification of the KC is found to drive nutrient-rich upwelling in the shelf regions, induce anomalous warming that leads to coastal marine heatwaves, and reduce the ability of the oceans to absorb anthropogenic carbon dioxide. Based on altimeter and in situ observations, we find an onshore acceleration and offshore deceleration of the KC over the past three decades. This intensification is characterized by a spatial mean onshore acceleration (offshore deceleration) of 0.39 (−0.63) cm s−1 per decade. This phenomenon can be attributed to changes in wind stress curl (WSC) and oceanic stratification over the subtropical North Pacific. The weakened WSC decreases the vertical extent of the KC by reducing its transport and contributes to the offshore deceleration, whereas the enhanced stratification drives the uplift of the KC and contributes to the onshore acceleration. Our findings underscore the importance of establishing and maintaining a long-term monitoring network for the zonal variations of the KC in the future to obtain a comprehensive understanding of the associated impacts.

Sampling efficiency of a polyurethane foam air sampler: Effect of temperature

Effective monitoring of atmospheric concentrations is vital for assessing the Stockholm Convention's effectiveness on persistent organic pollutants (POPs). This task, particularly challenging in polar regions due to low air concentrations and temperature fluctuations, requires robust sampling techniques. Furthermore, the influence of temperature on the sampling efficiency of polyurethane foam discs remains unclear. Here we employ a flow-through sampling (FTS) column coupled with an active pump to collect air samples at varying temperatures. We delved into breakthrough profiles of key pollutants, such as polycyclic aromatic hydrocarbons (PAHs), polychlorobiphenyls (PCBs), and organochlorine pesticides (OCPs), and examined the temperature-dependent behaviors of the theoretical plate number (N) and breakthrough volume (VB) using frontal chromatography theory. Our findings reveal a significant relationship between temperature dependence coefficients (KTN, KTV) and compound volatility, with decreasing values as volatility increases. While distinct trends are noted for PAHs, PCBs, and OCPs in KTN, KTV values exhibit similar patterns across all chemicals. Moreover, we establish a binary linear correlation between log (VB/m3), 1/(T/K), and N, simplifying breakthrough level estimation by enabling easy conversion between N and VB. Finally, an empirical linear solvation energy relationship incorporating a temperature term is developed, yielding satisfactory results for N at various temperatures. This approach holds the potential to rectify temperature-related effects and loss rates in historical data from long-term monitoring networks, benefiting polar and remote regions.

The Isotopic Composition of Rainfall on a Subtropical Mountainous Island

Abstract Tropical islands are simultaneously some of the most biodiverse and vulnerable places on Earth. Water resources help maintain the delicate balance on which the ecosystems and the population of tropical islands rely. Hydrogen and oxygen isotope analyses are a powerful tool in the study of the water cycle on tropical islands, although the scarcity of long-term and high-frequency data makes interpretation challenging. Here, a new dataset is presented based on weekly collection of rainfall H and O isotopic composition on the island of O‘ahu, Hawai‘i, beginning from July 2019 and still ongoing. The data show considerable differences in isotopic ratios produced by different weather systems, with Kona lows and upper-level lows having the lowest δ2H and δ18O values, and trade-wind showers the highest. The data also show significant spatial variability, with some sites being characterized by higher isotope ratios than others. The amount effect is not observed consistently at all sites. Deuterium excess shows a marked seasonal cycle, which is attributed to the different origin and history of the air masses that are responsible for rainfall in the winter and summer months. The local meteoric water line and a comparison of this dataset with a long-term historical record illustrate strong interannual variability and the need to establish a long-term precipitation isotope monitoring network for Hawai‘i. Significance Statement The isotopic composition of water is often used in the study of island water resources, but the scarcity of high-frequency datasets makes the interpretation of data difficult. The purpose of this study is to investigate the isotopic composition of rainfall on a mountainous island in the subtropics. Based on weekly data collection on O‘ahu, Hawai‘i, the results improve our understanding of the isotopic composition of rainfall due to different weather systems, like trade-wind showers or cold fronts, as well as its spatial and temporal variability. These results could inform the interpretation of data from other mountainous islands in similar climate zones.

Quo vadis Patria Gaucha? Uruguayan pathways of land use change

South American grasslands, socio-ecological systems used heavily for a long time, are currently experiencing dramatic land-use changes due to implementation of large-scale afforestation and agro-industrial cash crops. Applying the conceptual framework of “Multifunctional and sustainable productive landscapes” to Uruguay, we explored the impacts on rural ecosystems and communities based on a long-term monitoring network by assessing species richness of plant and terrestrial arthropods and socio-economic data from national census. We found that silvi- and agricultural industry established mainly at the expense of extensively grazed grasslands and local family farms with traditional techniques, accompanied by a deregulation of the rural labor market, depopulation and aging of rural society. Governmental nature protection efforts increase the native forest cover and establish nature protection areas focusing mainly on forests. We also discuss pathways of land-use change in recent decades and related discourses of local stakeholders.

Seguimiento de la biodiversidad en la era del Big Data

The monitoring and evaluation of the distribution, structure and functioning of biodiversity, as well as the effects exerted by different pressures and threats on its conservation and dynamics in a context of Global Change, constitute one of the greatest challenges of current science and a critical axis in the agendas of numerous government agencies. Given the importance of having reliable, representative and temporally dynamic data to respond to these challenges, Ecology, like other branches of Biology and Earth Sciences, has recently echoed the phenomenon known as "Big Data" or "Data Science". In Ecology, this massive dataset relates to several sources of information: a) time series of remote observation data; b) aggregation of local and regional field or experimental data; c) long-term monitoring networks with national and international field data; d) automated sensor networks, and, e) Citizen Science initiatives, among others. Together, Big Data amplifies the spatio-temporal scale of issues related to biodiversity monitoring and management, making it possible to cover aspects and scales that were unthinkable only a few years ago. However, its application in Ecology still presents great challenges and there is currently an intense debate about its applicability at scales related to the management of spaces and species. Through its pages, this review tries to present the current state of the science on monitoring biodiversity of terrestrial ecosystems and its sources of information, as well as its synergies, applications, analysis methodologies, challenges and opportunities in the era of Big Data.

Accumulation and vertical distribution of glomalin-related soil protein in French temperate forest soils as a function of tree type, climate and soil properties

Soil organic matter (SOM) is of critical importance to the functioning of ecosystems because of its effects on soil nutritional quality, microbial activity and soil structure. SOM is made up of a variety of compounds ranging from chemically reactive and mobile forms to stable, recalcitrant forms. An operationally defined fraction of soil organic matter known as glomalin-related soil protein (GRSP) is thought to be of fungal origin, very stable and responsible for increased physical stability of soil. To date, the origin of this fraction of SOM and the factors controlling its accumulation in soils are not well understood. The aim of this study was to contribute to the understanding of the origin of this fraction and the factors which contribute to its accumulation in the soil. This study was carried out on archived soils from 102 sites of the long-term monitoring network for forest ecosystems in France (RENECOFOR), from depths up to 1 m. The effects of tree type, climate and soil properties on the accumulation and vertical distribution of GRSP were assessed. GRSP was greater under conifer forests than broadleaf forests. GRSP in the top soil layer was positively correlated with both SOC and total nitrogen, and inversely related with pH, with the strongest effect observed at very acid (pH ≤ 4.0). Both GRSP and SOC were found to follow exponential declines with depth. The contrast in vertical distribution of GRSP and SOC supports the hypothesis that GRSP is a distinct fraction of SOM. Climate and soil properties had significant influence on the vertical distribution of GRSP. The accumulation of GRSP, and the enrichment of SOC in GRSP, at acid pH could indicate a fungal origin of GRSP.

Regional Potential Wind Erosion Simulation Using Different Models in the Agro-Pastoral Ecotone of Northern China.

Wind erosion is crucial for assessing regional ecosystem services and sustainable development. The Agro-Pastoral Ecotone of northern China (APEC) is a typical region undergoing wind erosion and soil degradation. In this study, the National Wind Erosion Survey Model of China, the Integrated Wind Erosion Modeling System, and the regional versions of the Revised Wind Erosion Equation and Wind Erosion Prediction System were used to evaluate the regional potential wind erosion of the APEC during 2000 and 2012. The results showed that the potential wind erosion predicted by National Wind Erosion Survey Model of China (NWESMC), Revised Wind Erosion Equation (RWEQ), Wind Erosion Prediction System (WEPS), and Integrated Wind Erosion Modeling System (IWEMS) were significantly related to the observed wind erosion collected from published literature, but the observed data were generally smaller than the predicted values. The average potential wind erosions were 12.58, 25.87, 52.63, and 58.72 t hm−2 a−1 for NWESMC, RWEQ, WEPS, and IWEMS, respectively, while the spatial pattern and temporal trend of annual potential wind erosion were similar for different wind erosion models. Wind speed, soil moisture, and vegetation coverage were the dominant factors affecting regional wind erosion estimation. These results highlight that it is necessary to comprehensively calibrate and validate the selected wind erosion models. A long-term standard wind erosion monitoring network is urgently required. This study can serve as a useful reference for improving wind erosion models.

Impacts of Permafrost Degradation on Hydrology and Vegetation in the Source Area of the Yellow River on Northeastern Qinghai-Tibet Plateau, Southwest China

Under a persistent warming climate and increasing human activities, permafrost in the Source Area of the Yellow River (SAYR) has been degrading regionally, resulting in many eco-environmental problems. This paper reviews the changes in air temperature and precipitation over the past 60 years and presents the distribution and degradation of alpine permafrost in the SAYR. The review is focused on the permafrost degradation–induced changes in hydrology, wetlands, thermokarst lakes, ponds, and vegetation. Mean annual air temperatures have been rising at an average rate of 0.4°C/10a over the past 60 years, while precipitation has increased only slightly (16 mm/10a). Borehole temperature monitoring at the depth of 15 m shows the permafrost warming rates of 0.01–0.21°C/10a in the Headwater Aera of the Yellow River. As a result of permafrost thaw, the amount of surface waters has declined while groundwater storage has increased. Due to permafrost degradation, the supra-permafrost water table lowers gradually, resulting in a reduction in areal extents of wetlands and lakes in the SAYR. We further renamed the concept of the burial depth of the ecologically-safe supra-permafrost water table, the minimum depth of the groundwater table for sustaining the normal growth of alpine grassland vegetation, for the SAYR to describe the relationship between the lowering permafrost table and succeeding alpine vegetation. Furthermore, we recommended more studies focusing on snow cover and carbon stock and emissions related to permafrost degradation under a warming climate. We also advised to timely establish the long-term monitoring networks for the rapidly changing mountain cryosphere, alpine ecology, alpine hydrology, eco-hydrology, cryo-hydrogeology, and carbon fluxes. Moreover, process-based models should be developed and improved to better simulate and predict the responses of alpine ecosystem changes to the interacting cryospheric and other environmental variables and their ecological and ecohydrological impacts in the SAYR and downstream Yellow River basins. This study can help better manage the ecological and hydrological environments in the Upper Yellow River that are sensitive to changes in the alpine climate and cryosphere.

Fire ecology for the 21st century: Conserving biodiversity in the age of megafire

Fire ecology for the 21st century: Conserving biodiversity in the age of megafire

UTILIZING STABLE WATER ISOTOPES (Δ2H AND Δ18O) TO STUDY SOIL-WATER ORIGIN IN SLOPED VINEYARD: FIRST RESULTS

The diversity of processes taking place in hillslope agro-ecosystems makes the estimation of vadose zone dynamics rather challenging. This paper presents the first insight into the research of volumetric water content, granulometric composition, meteorological data, precipitation and soil-water isotopic composition conducted within the SUPREHILL project at its vadose zone observatory. The main goals of this research are related to the evaluation of soil-water origin at the hillslope vineyard, but also to the estimation of depths until which precipitation infiltrates and where the occurrence of preferential flow is possible. For that purpose, hydrometeorological data, granulometric composition and stable isotopesof hydrogen (δ2H) and oxygen (δ18O) from precipitation and sampled soil water have been used. The results indicate the existence of a different isotopic signature in soil water, which suggests different infiltration patterns in the investigated area. Also, the results point out that surface runoff, subsurface runoff, and most of the passive wick lysimeters respond to precipitation, while the response of suction probes located at deeper depth is not that evident. This corresponds to the results related to the variation of water content at different depths. All the results indicate the possible existence of a low permeable layer at an approximate depth of 60 cm. Furthermore, preferential flow, if it exists, can be expected from the shallowest depths of the vineyard to a maximum depth of 80 cm. It is expected that an established long-term monitoring network at the SUPREHILL Observatory will give a more precise definition of soil-water behaviour and the existence of preferential flow.

Source Level of Antarctic Blue and Fin Whale Sounds Recorded on Sonobuoys Deployed in the Deep-Ocean Off Antarctica

The source levels, SL, of Antarctic blue and fin whale calls were estimated using acoustic recordings collected from directional sonobuoys deployed during an Antarctic voyage in 2019. Antarctic blue whale call types included stereotyped song and downswept frequency-modulated calls, often, respectively, referred to as Z-calls (comprising song units-A, B, and C) and D-calls. Fin whale calls included 20 Hz pulses and 40 Hz downswept calls. Source levels were obtained by measuring received levels (RL) and modelling transmission losses (TL) for each detection. Estimates of SL were sensitive to the parameters used in TL models, particularly the seafloor geoacoustic properties and depth of the calling whale. For our best estimate of TL and whale-depth, mean SL in dB re 1 μPa ± 1 standard deviation ranged between 188–191 ± 6–8 dB for blue whale call types and 189–192 ± 6 dB for fin whale call types. These estimates of SL are the first from the Southern Hemisphere for D-calls and 40 Hz downsweeps, and the largest sample size to-date for Antarctic blue whale song. Knowledge of source levels is essential for estimating the detection range and communication space of these calls and will enable more accurate comparisons of detections of these sounds from sonobuoy surveys and across international long-term monitoring networks.

Enabling the Reuse of Long-Term Marine Biological Observations in Essential Variables Frameworks Through a Practical Approach

Essential Biodiversity Variables (EBVs) and Biological and Ecosystem Essential Ocean Variables (BioEco EOVs) are two cooperative conceptual frameworks which help harmonize and process multi-source marine biodiversity observations into robust indexes, in order to measure progress toward policy conservation goals. Long-term monitoring networks are encouraged to contribute to these frameworks by mobilizing historical times series which are suitable for detecting impacts of management policies. In this paper, we identify specific recommendations for increasing reuse in the EV frameworks of the biodiversity historical data collected and maintained by the Gulf of Venice (GOV) site, i.e., the monitoring facility that is selected as case study in the Italian Long-Term Ecological Research network (LTER-Italy). The recommendations are obtained through a practical approach comprising two phases. In the first phase, a literature review helps extract the guidelines for implementing the principles representing the most recent attempt to unify management of EBV and BioEco EOV data, i.e., Benson’s tenets. In the second phase, we compare the guidelines to the data management practices enacted by the selected monitoring site in order to recommend curation interventions. The outputs of the analysis are discussed in order to verify if the approach and the recommendations are general enough to be replicated in the marine component of monitoring networks to coordinate the LTER data contribution to the EV frameworks.

Measuring the unseen: mobilizing citizen scientists to monitor groundwater in Nepal

Groundwater-level monitoring provides crucial information on the nature and status of aquifers and their response to stressors like climate change, groundwater extraction, and land use changes. Therefore, the development of a spatially distributed long-term monitoring network is indispensable for sustainable groundwater resource management. Despite being one of our greatest unseen resources, groundwater systems are too often poorly understood, ineffectively managed, and unsustainably used. This study investigates the feasibility of establishing a groundwater monitoring network mobilizing citizen scientists. We established a network of 45 shallow monitoring wells in the Kathmandu Valley using existing wells. We recruited 75% of the citizen scientists through personal connections and the rest through outreach programs at academic institutes and site visits. We used various methods to encourage citizen scientists to complete regular measurements and solicited feedback from them based on their experiences. Citizen scientists were more consistent during the monsoon season (June through September) than non-monsoon seasons. The depth-to-water below the ground surface varied from − 0.11 m (negative sign represents a groundwater level higher than the ground surface) to 11.5 m, with a mean of 4.07 m and standard deviation of 2.63 m. Groundwater levels began to rise abruptly with the onset of monsoon season and the shallowest and the deepest groundwater levels were recorded in peak rainfall months and dry months respectively. Citizen science-based groundwater monitoring using existing wells would be an economic and sustainable approach for groundwater monitoring. Improved groundwater-level data will provide essential information for understanding the shallow groundwater system of the valley, which will assist concerned authorities in planning and formulating evidence-based policy on sustainable groundwater management.

Rapid soil and vegetation changes at regional scale in continental Antarctica

Antarctica is the last pristine environment on Earth, its biota being adapted to the harsh and extreme polar climate. Until now, soil formation and vegetation development in continental Antarctica were considered very slow due to the extreme conditions of this polar desert. Since the austral summer 2002/2003, a long-term monitoring network of the terrestrial ecosystems (soils, vegetation, active layer thickness) has been established at Victoria Land (VL) across a > 500 km latitudinal gradient of coastal sites (73°–77°S). In only one decade large ecosystem changes were detected. Climate was characterized by a significant increase of thawing degree days in northern VL and of autumn air temperature. No extreme climatic events (such as hot spells) where detected in the study period. Soil chemistry suffered large quantitative changes, clearly indicating rapid pedogenetic processes. In most soils the upper layers exhibited a strong alkalinization (pH increases up to 3 units) and increases in conductivity, anions and cations (in particular of SO4 and Na). The largest changes were observed in soils with low vegetation cover. Statistically significant differences in soil chemistry were detected between soils with high and low vegetation cover, the former showing lower pH, conductivity, Na and Cl. Most plots exhibited changes of total cover, species richness and floristic composition, with vegetation expansion in soils with low vegetation cover and the largest increase recorded at Apostrophe Island (northern VL). Principal Component Analysis (PCA) identified the main trend of vegetation change, with a shift from lower to higher cover and a secondary trend of change associated with a gradient of water availability, consistent with an increase in water instead of snow. Redundancy analysis (RDA) identified the trend of change in soil chemistry with increases in pH, conductivity, anions and cations associated with the concomitant decrease in C, N, NO3, PO4. The RDA confirmed that soil changes were associated with a gradient of vegetation change (from low to high cover) as well as of water availability, as already indirectly outlined by the PCA. Field manipulation experiments carried out at five locations of the network between 73°S and 77°S, simulating increases of precipitation from snow or water additions didn’t induce changes in soil pH, indicating that pulse events of snow accumulation or melting could not trigger persistent soil pH changes. These data allow hypothesize the occurrence of a main ecosystem change occurring at regional scale at Victoria Land. The slight air warming and its consequences on soil chemistry and vegetation, further highlight the sensitivity of the fragile Antarctic ecosystems to the consequences of even small changes in climate.

Numerical Simulations of Non-Point Source Pollution in a Small Urban Catchment: Identification of Pollution Risk Areas and Effectiveness of Source-Control Measures

Urban non-point source pollution is becoming a serious issue under the context of rapid urbanization and its impacts on surface hydrologic processes. The identification of non-point source risk areas and the effectiveness of source-control measures provides important first steps to improve the degrading aquatic environment but is challenged by the complex dynamics and variabilities of surface pollutants in urban environments. In this study, we investigate the spatial and temporal variabilities of non-point source pollution in a small urban catchment based on numerical simulations and in-situ samplings. Our results show that residential, industrial, and commercial land contribute to the most pollutant loadings and are the main constituents of the pollution risk area. Rainfall duration and intensity are the main factors in determining the temporal variations of urban non-point source pollution. There is no correlation between early drought days and pollution load. Numerical simulations show that it is more effective to increase urban vegetation coverage than to enhance road cleaning for effective non-surface pollution control. For enhanced road cleaning, it is more effective to improve the frequency of road cleaning than its efficiency. Our results provide important guidance for effective controls of non-point source pollution as well as the establishment of long-term surface pollutant monitoring network in complex urban environments.

Comunidades de invertebrados terrestres del archipiélago Diego Ramírez (56°31’S), el sitio de estudios ecológicos de largo plazo más austral de américa: Diversidad y afinidades con las islas subantárticas del océano austral

The Diego Ramirez and Cape Horn archipelagos are located at the southern end of the Magellanic subantarctic ecoregion. The fauna of insects and other terrestrial invertebrates has been poorly characterized. In this work, we present an updated assessment of invertebrates, with a focus on the terrestrial entomofauna of the Diego Ramirez Archipelago. We reviewed biogeographic affinities of this southern archipelago with the rest of the subantarctic islands. We found that Gonzalo Island in the Diego Ramirez Archipelago is free of insect species and other exotic invertebrates. The island’s terrestrial invertebrate fauna registered during this study includes 32 taxa, mainly from the Class Insecta, which are distributed in different habitats, being the communities of Poa flabellata the most important habitats. The entomofauna of the Diego Ramirez Archipelago shows a low total similarity between the fauna reported and the rest of the islands, except with South Georgia. However, the biota that links them is of Gondwanic origin, which suggests the existence of ancient vicariant biogeographic connections. This work is a contribution to the development, strengthening and inauguration of the Cape Horn Long-Term Ecological Monitoring Network (LTER Cape Horn Network). The particular focus on the Diego Ramirez Islands contributes directly to filling a “blind spot” in our current knowledge of the effects of global environmental change in sub-Antarctic ecosystems, generating information essential to their conservation in the short, medium and long term.

Temporal trends in tree defoliation and response to multiple biotic and abiotic stresses

The vitality of forests depends on multiple biotic and abiotic stresses that can act in an interactive way. Tree defoliation levels are therefore subject to long-term changes and shorter-term hazards that need to be monitored in the context of ongoing climate change. In this study, we analysed the combined effects of drought, insect attack and tree nutritional status on the level of defoliation in three major hardwood species in Europe: European beech (Fagus sylvatica), sessile oak (Quercus petraea) and pedunculate oak (Quercus robur). The forest condition data set was collected in the long-term intensive monitoring network in France (RENECOFOR). The average level of defoliation observed was 20% but varied considerably between plots and trees. From 1997 to 2015, beech defoliation worsened by 10% while oak defoliation stabilized over time. For the three tree species, crown defoliation was generally higher in the event of insect attack (increased by 2.6% to 7.5% depending on the tree species) and under drought (increased by 5.9%), while the effect of the tree nutritional statue was less consistent (from −5.6% to +10%) these factors acting synergistically. This study highlights the fact that the different stresses a tree species undergoes act in a complex and interactive way, with species-specific responses. In a context of increasing abiotic and biotic stresses, their combined analysis appears to be a necessity at a time when forest owners need to adapt their management to cope with climate change, particularly through the choice of tree species to be favoured in the future.

Setting the basis for a long-term monitoring network of intertidal seaweed assemblages in northwest Spain

A distortion of coastal communities has been reported along the European Atlantic in recent years. In NW Spain, the lack of studies focusing on long-term changes was resolved when several common perennial seaweeds were shown to have diminished in occurrence between 1998/99 and 2014. To ascertain whether their decline reflected a genuine long-term trend, the same network of monitoring locations and the same set of perennial seaweeds was re-surveyed in 2018. Contrary to our expectations, the average number of species per site increased in semi-exposed and semi-sheltered locations to become statistically indistinguishable from 1998/99 estimates. Nevertheless, site occupancy rates continued to be below 1998/99 estimates for several seaweeds, and warming, both from rising average temperatures and from more frequent and intense marine heatwaves in autumn, seems a plausible explanation for their decline. The benefits of routinely monitoring a network of fixed stations, especially when they are subject to different levels of wave exposure, are discussed.

Fewer sites but better data? Optimising the representativeness and statistical power of a national monitoring network

Indicators of large-scale ecological change are typically derived from long-term monitoring networks. As such, it is important to assess how well monitoring networks provide evidence for ecological trends in the regions they are monitoring. In part, this depends on the network’s representativeness of the full range of environmental conditions occurring in the monitored region. In addition, the statistical power to detect trends and ecological changes using the network depends on its structure, size and the intensity and accuracy of monitoring. This paper addresses the optimisation of representativeness and statistical power when re-designing existing large-scale ecological monitoring networks, for example due to financial constraints on monitoring programmes. It uses a real world example of a well-established river monitoring network of 254 sites distributed across Scotland. We first present a novel approach for assessing a monitoring network’s representativeness of national habitat and pressure gradients using the multivariate two-sample Cramér’s T statistic. This compares multivariate gradient distributions among sites inside and outside of the network. Using this test, the existing network was found to over-represent larger and more heavily polluted sites, reflecting earlier research priorities when it was originally designed. Network re-design was addressed through stepwise selection of individual sites to remove from or add to the network to maximise multivariate representativeness. This showed that combinations of selective site retention and addition can be used to modify existing monitoring networks, changing the number of sites and improving representativeness. We then investigated the effect of network re-design on the statistical power to detect long-term trends across the whole network. The power analysis was based on linear mixed effects models for long-term trends in three ecological indicators (ecological quality ratios for diatoms, invertebrates and macrophytes) over a ten-year period. This revealed a clear loss of power in smaller networks with less accurate sampling, but sampling schedule had a smaller effect on power. Interestingly, more representative networks had slightly lower trend detection power than the current unrepresentative network, though they should give a less biased estimate of national trends. Our analyses of representativeness and statistical power provide a general framework for designing and adapting large-scale ecological monitoring networks. Wider use of such methods would improve the quality of indicators derived from them and improve the evidence base for detecting and managing ecological change.