Changes In Ecosystem Function Research Articles

Changes in leaf litter decomposition of primary Korean pine forests after degradation succession into secondary broad-leaved forests.

Forest degradation succession often leads to changes in forest ecosystem functioning. Exactly how the decomposition of leaf litter is affected in a disturbed forest remains unknown. Therefore, in our study, we selected a primary Korean pine forest (PK) and a secondary broad‐leaved forest (SF) affected by clear‐cutting degradation, both in Northeast China. The aim was to explore the response to changes in the leaf litter decomposition converting PK to SF. The mixed litters of PK and SF were decomposed in situ (1 year). The proportion of remaining litter mass, main chemistry, and soil biotic and abiotic factors were assessed during decomposition, and then, we made an in‐depth analysis of the changes in the leaf litter decomposition. According to our results, leaf litter decomposition rate was significantly higher in the PK than that in the SF. Overall, the remaining percent mass of leaf litter's main chemical quality in SF was higher than in PK, indicating that leaf litter chemical turnover in PK was relatively faster. PK had a significantly higher amount of total phospholipid fatty acids (PLFAs) than SF during decomposition. Based on multivariate regression trees, the forest type influenced the soil habitat factors related to leaf litter decomposition more than decomposition time. Structural equation modeling revealed that litter N was strongly and positively affecting litter decomposition, and the changes in actinomycetes PLFA biomass played a more important role among all the functional groups. Selected soil abiotic factors were indirectly driving litter decomposition through coupling with actinomycetes. This study provides evidence for the complex interactions between leaf litter substrate and soil physical–chemical properties in affecting litter decomposition via soil microorganisms.

Assessing change in habitat composition, ecosystem functioning and service supply in Latvian protected stony reefs

Healthy and diverse marine ecosystems are a source of a whole range of ecosystem services (ES) and social, and economic benefits. To preserve and restore biodiversity, and sustain service supply, an international goal was set to protect at least 10 % of the global coastal and marine area by 2020. The goal has been achieved mainly through the designation of marine protected areas (MPAs). Whilst activities within the MPAs can be restricted to manage local pressures, the protected habitats and species are still exposed to stressors that originate outside MPA borders (e.g., non-native species, eutrophication). This study investigates the change in the protected stony reef habitat composition using underwater video observation in the coastal area of the eastern Baltic Sea known to be under the pressure of a non-native fish species. Further, assesses what the observed changes have meant for ecosystem functioning and ES supply adopting a tailor-made, expert judgement-based ES supply assessment method developed during the BONUS BASMATI project. The results suggest that the quality of the protected habitats in the case study sites has deteriorated and the transformation in species composition has altered ecosystem functioning and ES supply. The study highlights the importance of rich and diverse habitats for human wellbeing and livelihoods. Further, emphasises the need for more stringent MPA management plans, as well as a wider ecosystem-based approach to decision making in order to limit the impacts of stressors on marine ecosystems and secure ES supply.

Land cover change-induced decline in terrestrial gross primary production over the conterminous United States from 2001 to 2016

As one of the most dynamic aspects of global environmental change, land cover change (LCC) has a profound impact on terrestrial carbon sequestration. However, LCC-induced carbon fluxes are still the most uncertain terms in global and regional carbon budgets. Ecosystem gross primary production (GPP) is the total carbon uptake by vegetation through photosynthesis, serving as a major control on ecosystem function and land carbon balance during and after the modification of the land surface. However, accurately capturing LCC-induced GPP changes requires both high-quality land cover data and controlling for variation driven by other environmental factors such as climate. In this study, we comprehensively examined the effects of LCC on annual GPP trends over the conterminous United States (CONUS) from 2001 to 2016 using the USGS National Land Cover Database, a remote sensing-driven ecosystem model, and the Google Earth Engine cloud computing platform. We designed a series of model experiments to identify LCC effects on GPP by controlling climate effects. During the study period, LCC exerted a strong negative effect on total GPP across the CONUS ([-2.2, -1.8] Tg C yr−2), while climate had smaller positive effects ([0.17, 0. 92] Tg C yr−2). The LCC-induced reduction of GPP was mainly caused by net forest loss ([-1.98, -1.39] Tg C yr−2) and urban expansion ([-2.03, -1.92] Tg C yr−2), but was partially offset by increases in crop area ([+0.66, +0.79] Tg C yr−2). Ensemble simulations from TRENDY did not capture the strong negative LCC influences on GPP, likely due to limitations of the adopted land use/cover data. Our study provides a novel perspective on LCC-induced GPP changes, which could help to improve our understanding of ecosystem function changes and constrain the estimation of land carbon balance in the context of anthropogenic activity and climate change.

Human landscape modification and expansion of tropical woodland in southern Arabia during the mid‐Holocene from rock hyrax middens

AbstractAimDryland ecosystems, such as those in southern Arabia, are particularly vulnerable to climate and land‐use change. Aridification and human subsistence changes at the end of the Holocene Humid Period at 6–4 ka have been used as an iconic example for evaluating such impacts to resilience of arid systems. Although records of ancient environments can provide critical insight into the biotic and abiotic mechanisms that alter ecosystems, traditional archives, such as lake deposits, are not common in southern Arabia after 6 ka; thus, we must use alternative archives.LocationYemen.TaxonPlants; Rock Hyrax (Procavia capensis).MethodsWe use fossil pollen and stable isotopes (δ15N; δ13C) of rock hyrax (P. capensis) middens from Wadi Sana, Yemen, to look at changes in ecosystem structure and function across this key transition from 6 ka to the present. A total of 17 middens were radiocarbon‐dated and stable isotopes were measured. Of these, pollen was extracted from hyraceum of 14 middens and identified using a light microscope. Fossil pollen assemblages were then compared to existing modern pollen samples from throughout Arabia.ResultsDuring the mid‐Holocene from at least 6 to 4.7 ka, the pollen flora reflects a landscape with abundant tropical trees. These included foundational woody taxa, such as Terminalia and Boswellia sacra (frankincense), which had a strong positive influence on local hydrology and the economy, respectively. Increased charcoal abundances also suggest that wildfire occurred periodically.Main conclusionsConnections with archaeological evidence suggest a strong link between human management and the presence of Terminalia woodland during the mid‐Holocene. These may have promoted increased groundwater storage and ponding as regional rainfall was decreasing. The mid‐Holocene expansion of Boswellia sacra (frankincense) may have helped support resin trade that became a critical export from the region. Fires were more common than today, suggesting semi‐arid but continuous vegetation cover across what is now bare ground. Finally, after 1 ka, increased sedge abundances at the expense of grasses and trees suggest the development of desert conditions.

Effect of limited compaction on soil solution chemistry in two acidic forest ecosystems: Changes, recovery and impact of liming

Forest practices are rapidly becoming mechanised in France, resulting in unknown consequences for the current and long-term functioning and functions of ecosystems. Degradation of forest soil porosity cannot be remediated artificially, and restoration via natural processes is slow and not likely to include deep soil layers, where tree roots take up large amounts of water and nutrients. In 2007 and 2008, two experimental sites were set up in the Lorraine Plateau (France). The soils are Ruptic Luvisols and are classified as highly sensitive to compaction. We observed multiple parameters and studied weakly bound soil solutions, which are known to react to changes in ecosystem functioning. We hypothesised that (i) soil solution chemistry is a relevant indicator to assess soil changes after compaction and dynamics of soil recovery in the decade following compaction, (ii) restoration is greater at the more fertile site and (iii) soil pH is a relevant parameter to explain the behaviour of soil solutions. Our results showed that soil solution concentrations changed drastically after compaction and that restoration was more effective in the less fertile soil than in the more fertile one. Finally, a soil pH threshold of 4.5 was relevant for explaining the behaviour of nitrate, which is particularly useful for monitoring solution geochemistry in these acidic soils. Liming at the less fertile site increased the pH to more than 4.5, which changed the behaviour of nitrate and reinforced the utility of this threshold for explaining soil biogeochemical functioning. Soil solution is a relevant indicator of current soil functioning after compaction; however, this study demonstrated that additional information is required to understand its meaning accurately. This study highlights that long-term observation is needed to identify the consequences of soil compaction on long-living ecosystems.

The Climatological Rise in Winter Temperature- and Dewpoint-Based Thaw Events and Their Impact on Snow Depth on Mount Washington, New Hampshire

AbstractWe analyze how winter thaw events (TE; T>0°C) are changing on the summit of Mount Washington, New Hampshire using three metrics: the number of TE, number of thaw hours, and number of thaw degree-hours for temperature and dewpoint for winters from 1935-36 to 2019-20. The impact of temperature-only-TE and dewpoint-TE on snow depth are compared to quantify the different impacts of sensible-only and sensible-and-latent heating, respectively. Results reveal that temperature- and dewpoint-TE for all metrics increased at a statistically significant rate (p<0.05) over the full time periods studied for temperature (1935-1936 to 2019-2020) and dewpoint (1939-1940 to 2019-2020). Notably around 2000-2001, the positive trends increased for most variables, including dewpoint thaw degree-hours that increased by 82.11 degree-hours decade-1during 2000-2020 – about five times faster than the 1939-2020 rate of 17.70 degree-hours decade-1. Furthermore, a clear upward shift occurred around 1990 in the lowest winter values of thaw hours and thaw degree-hours – winters now have a higher baseline amount of thaw than before 1990. Snow depth loss during dewpoint-TE (0.36 cm hr-1) occurred more than twice as fast as temperature-only-TE (0.14 cm hr-1). With winters projected to warm throughout the 21stcentury in the Northeastern US, it is expected that the trends in winter thaw events, and the sensible and latent energy they bring, will continue to rise and lead to more frequent winter flooding, fewer days of good quality snow for winter recreation, and changes in ecosystem function.

Linear Disturbances Shift Boreal Peatland Plant Communities Toward Earlier Peak Greenness

AbstractVast areas of boreal peatlands are impacted by linear disturbances known as seismic lines. Tree removal and ground disturbance alter vegetation communities and are expected to change ecosystem functioning. As boreal landscapes continue to be disturbed by linear disturbances, understanding the magnitude and mechanisms of vegetation and phenology changes is the first step toward predicting carbon cycling changes across broad spatial scales. We investigate seismic line disturbances on peatland plant community composition and phenological patterns using readily available digital photography at a bog and a fen in Alberta, Canada. Our objectives were to: (a) compare the understory peatland vegetation on seismic lines with those in adjacent undisturbed areas using two phenological metrics (green and red chromatic coordinates); (b) evaluate if vegetation greenness is directly related to vegetation community composition, and (c) determine whether plot‐scale greenness predicts plant productivity. We found that areas of peatlands intersected by seismic lines have an earlier seasonal peak (maximum greenness) compared to undisturbed areas, and vegetation communities had a stronger relationship to greenness and gross primary production (GPP) at disturbed areas relative to undisturbed areas. This change in understory vegetation results in greater CO2 uptake in disturbed areas. We demonstrate an easy‐to‐use application of digital photography that successfully quantifies phenological changes in boreal peatland vegetation. This nondestructive method for understanding vegetation phenology eliminated the need for fixed infrastructure and allowed us to expand our sampling capacity and study sites while allowing for repeated measures in the future.

Monitoring restored tropical forest diversity and structure through UAV-borne hyperspectral and lidar fusion

Remote sensors, onboard orbital platforms, aircraft, or unmanned aerial vehicles (UAVs) have emerged as a promising technology to enhance our understanding of changes in ecosystem composition, structure, and function of forests, offering multi-scale monitoring of forest restoration. UAV systems can generate high-resolution images that provide accurate information on forest ecosystems to aid decision-making in restoration projects. However, UAV technological advances have outpaced practical application; thus, we explored combining UAV-borne lidar and hyperspectral data to evaluate the diversity and structure of restoration plantings. We developed novel analytical approaches to assess twelve 13-year-old restoration plots experimentally established with 20, 60 or 120 native tree species in the Brazilian Atlantic Forest. We assessed (1) the congruence and complementarity of lidar and hyperspectral-derived variables, (2) their ability to distinguish tree richness levels and (3) their ability to predict aboveground biomass (AGB). We analyzed three structural attributes derived from lidar data—canopy height, leaf area index (LAI), and understory LAI—and eighteen variables derived from hyperspectral data—15 vegetation indices (VIs), two components of the minimum noise fraction (related to spectral composition) and the spectral angle (related to spectral variability). We found that VIs were positively correlated with LAI for low LAI values, but stabilized for LAI greater than 2 m2/m2. LAI and structural VIs increased with increasing species richness, and hyperspectral variability was significantly related to species richness. While lidar-derived canopy height better predicted AGB than hyperspectral-derived VIs, it was the fusion of UAV-borne hyperspectral and lidar data that allowed effective co-monitoring of both forest structural attributes and tree diversity in restoration plantings. Furthermore, considering lidar and hyperspectral data together more broadly supported the expectations of biodiversity theory, showing that diversity enhanced biomass capture and canopy functional attributes in restoration. The use of UAV-borne remote sensors can play an essential role during the UN Decade of Ecosystem Restoration, which requires detailed forest monitoring on an unprecedented scale.

The growth of plants and indigenous bacterial community were significantly affected by cadmium contamination in soil\u2013plant system

Concentrations of heavy metals continue to increase in soil environments as a result of both anthropogenic activities and natural processes. Cadmium (Cd) is one of the most toxic heavy metals and poses health risks to both humans and the ecosystem. Herein, we explore the impacts of Cd on a soil–plant system composed of oilseed rapes (Brassica napus and Brassica juncea) and bacteria. The results showed that Cd accumulation within tissues of two species of oilseed rapes enhanced with increasing concentrations of Cd in soils, and Cd treatment decreased their chlorophyll content and suppressed rapeseeds growth. Meanwhile, Cd stress induced the changes of antioxidative enzymes activities of both B. napus and B. juncea. Response to Cd of bacterial community was similar in soil-two species of oilseed rapes system. The impact of Cd on the bacterial communities of soils was greater than bacterial communities of plants (phyllosphere and endophyte). The α-diversity of bacterial community in soils declined significantly under higher Cd concentration (30 mg/kg). In addition, soil bacterial communities composition and structure were altered in the presence of higher Cd concentration. Meanwhile, the bacterial communities of bulk soils were significantly correlated with Cd, while the variation of rhizosphere soils bacterial communities were markedly correlated with Cd and other environmental factors of both soils and plants. These results suggested that Cd could affect both the growth of plants and the indigenous bacterial community in soil–plant system, which might further change ecosystem functions in soils.

How effective is direct seeding to restore the functional composition of neotropical savannas?

Species loss leads to changes in ecosystem function and services, impacting human well‐being. Although biodiversity restoration is pivotal to circumvent this situation, the techniques for restoring old‐growth savannas are still limited and the restoration outcomes remain unpredictable. Here, we use a trait‐based approach to understand the functional outcomes of ecological restoration via direct seeding in a Brazilian savanna (cerrado, hereafter neotropical savanna). We compared the functional composition from woody and non‐woody component, total biomass, and biomass allocation of a restored relative to a degraded savanna (abandoned pasture) dominated by exotic grasses and a well‐preserved old‐growth native savanna. We found that the functional composition of restored communities was very similar to those dominated by exotic grasses, both characterized by a greater dominance of species with acquisitive traits, higher above‐ground biomass, and lower investment in root biomass. In contrast, the native vegetation exhibited a dominance of conservative traits and higher investment in belowground rather than aboveground biomass. Even though the acquisitive traits in the restored savanna allow a fast aboveground biomass accumulation and soil cover, the lower belowground biomass investment in the restored savanna may limit its resistance and resilience to droughts and fires. Our findings suggest that restoration efforts in neotropical savanna should focus on fostering the establishment of slow‐growing species to recover the ecosystem properties provided by the high biodiversity in neotropical savannas.

Win some, lose some: Mesocosm communities maintain community productivity despite lower phosphorus availability because of increased species diversity

AbstractAimsThe restoration of degraded ecosystems typically focuses on establishing assemblages of target species, but successful recovery should also be evaluated by the ecosystem's functioning to guarantee long‐term persistence. We investigated how the processes underlying community assembly (i.e. species loss, species gain and changes in abundance of resident species) influenced ecosystem functioning in experimental grassland communities in different states of restoration.LocationA greenhouse experiment in northern Flanders, Belgium.MethodsWe set up a mesocosm experiment with communities of 19 planted species, ranging from slow‐growing species from poorly productive Nardus grasslands to fast‐growing species from highly productive Lolium perenne grasslands. We categorised the mesocosms into different grassland restoration states based on known abiotic and biotic restoration barriers for semi‐natural grassland restoration: soil phosphorus levels and soil biota communities. After two growing seasons, we used the CAFE approach, an ecological application of the Price equation, to partition the effects of plant community assembly on ecosystem functioning (here community productivity) for the different restoration states.ResultsAdding soil biota communities sampled from reference Nardus grasslands vs more intensively managed grasslands did not have a significant effect on either plant species richness or biomass productivity. Lower soil phosphorus concentrations (i.e. abiotic restoration) resulted in a higher plant species richness. However, the net effect on productivity was close to zero. The increase in productivity caused by species gains was compensated through decreases in productivity caused by species loss and by decreases in the abundance or functioning of species that are present in both abiotically degraded and abiotically restored states.ConclusionsNot only species richness but also species identity resulted in changes in ecosystem functioning (i.e. productivity), even though the net functional effects were close to zero. More specifically, we found that species richness‐driven increases in productivity were counterbalanced by resource‐driven and species identity‐driven reductions in productivity.

Trait-based filtering mediates the effects of realistic biodiversity losses on ecosystem functioning

Biodiversity losses are a major driver of global changes in ecosystem functioning. While most studies of the relationship between biodiversity and ecosystem functioning have examined randomized species losses, trait-based filtering associated with species-specific vulnerability to drivers of diversity loss can strongly influence how ecosystem functioning responds to declining biodiversity. Moreover, the responses of ecosystem functioning to diversity loss may be mediated by environmental variability interacting with the suite of traits remaining in depauperate communities. We do not yet understand how communities resulting from realistic diversity losses (filtered by response traits) influence ecosystem functioning (via effect traits of the remaining community), especially under variable environmental conditions. Here, we directly test how realistic and randomized plant diversity losses influence productivity and invasion resistance across multiple years in a California grassland. Compared with communities based on randomized diversity losses, communities resulting from realistic (drought-driven) species losses had higher invasion resistance under climatic conditions that matched the trait-based filtering they experienced. However, productivity declined more with realistic than with randomized species losses across all years, regardless of climatic conditions. Functional response traits aligned with effect traits for productivity but not for invasion resistance. Our findings illustrate that the effects of biodiversity losses depend not only on the identities of lost species but also on how the traits of remaining species interact with varying environmental conditions. Understanding the consequences of biodiversity change requires studies that evaluate trait-mediated effects of species losses and incorporate the increasingly variable climatic conditions that future communities are expected to experience.

Maine's Ecological Reserves: A Scientific Wellspring for Monitoring Natural Forest Dynamics

Maine's Ecological Reserve system provides an important baseline for monitoring changes in ecosystem composition and function in a relatively unmanaged landscape setting. Ecological reserves are areas where timber harvesting and other forms of resource extraction are prohibited, and where natural disturbances may proceed without significant human influence. Since 2002, the Maine Natural Areas Program and The Nature Conservancy have been conducting a continuous forest inventory in Maine's ecological reserves and encouraging the use of inventory data in research projects.

Urbanization reduces resource use efficiency of phytoplankton community by altering the environment and decreasing biodiversity

Urbanization often exerts multiple effects on aquatic and terrestrial organisms, including changes in biodiversity, species composition and ecosystem functions. However, the impacts of urbanization on river phytoplankton in subtropical urbanizing watersheds remain largely unknown. Here, we explored the effects of urbanization on phytoplankton community structure (i.e., biomass, community composition and diversity) and function (i.e., resource use efficiency) in a subtropical river at watershed scale in southeast China over 6 years. A total of 318 phytoplankton species belonging into 120 genera and 7 phyla were identified from 108 samples. Bacillariophyta biomass showed an increasing trend with increasing urbanization level. The phytoplankton community shifted from Chlorophyta dominance in rural upstream waters to Bacillariophyta dominance in urbanized downstream waters. Furthermore, phytoplankton diversity and resource use efficiency (RUE = phytoplankton biomass/total phosphorus) were significantly decreased with increasing urbanization level from upstream to downstream. Phytoplankton RUE exhibited a significant positive correlation with species richness, but a negative correlation with phytoplankton evenness. The variation in environmental factors (turbidity, total nitrogen, NH4+-N, total phosphorus, PO43−-P and percentage urbanized area) was significantly correlated with phytoplankton diversity and RUE. Overall, our results revealed the influence of urbanization on phytoplankton community structure and ecosystem function was due to its altering the environmental conditions. Therefore, human-driven urbanization may play crucial roles in shaping the structure and function of phytoplankton communities in subtropical rivers, and the mechanism of this process can provide important information for freshwater sustainable uses, watershed management and conservation.

Warming as a Driver of Vegetation Loss in the Sonoran Desert of California

AbstractDryland ecosystems cover large regions of the Earth and have important impacts on global biogeochemistry and the carbon cycle. The plant species that occupy dryland environments have traits that enable them to withstand harsh environmental conditions, and some researchers have hypothesized that dryland vegetation may be comparatively resilient to changing climate, while others have pointed out that dryland vegetation often operates close to the physiological limits of many species, implying a possible vulnerability to warming. Here we use the Landsat archive to analyze vegetation dynamics for part of the Sonoran Desert and adjacent mountains in southern California. We show that large decreases in vegetation cover occurred over the last 34 years (1984–2017), especially across the xeric portions of our study region, where we observed a normalized difference vegetation index (NDVI) decline of 1.1 ± 0.3% yr−1. Changes in precipitation explain most of the year‐to‐year variation but are unable to fully explain the observed long‐term decline in NDVI. Statistical models that combined summer temperature and mean annual precipitation explained more of the spatial and temporal structure of NDVI trends and implicate climate warming as an important driver of declining vegetation cover. The impact of warming contributed to a change in the precipitation‐vegetation relationship through time for this desert region, indicating a structural change in ecosystem function during the study period. These results suggest that recent climate change has already had significant impact on these drylands and highlight the potential for future warming to increase risks for dryland ecosystems in other regions.

Distribution of crayfish in the Southern Basin of Lake Michigan and the Greater Chicago Region

Crayfish represent important links in aquatic food webs because they have diverse, omnivorous diets and are an important source of energy for fishes and birds. Crayfish have the ability to increase sediment transport through bioturbation, some are considered ecosystem engineers due to their burrowing habits, and crayfish invasions have been linked to large declines in biodiversity and changes in ecosystem structure and function. Despite their ecological importance and the threats that invasive crayfishes pose, the distribution of crayfishes in the Laurentian Great Lakes is not well studied. Here, we report on four years of intensive crayfish surveys in the southwestern portion of the Lake Michigan Basin, a region with diverse freshwater ecosystems and few previous records of crayfish distribution. From 2015 to 2018, baited minnow traps and SCUBA were used to document the distribution and abundance of crayfish across streams, rivers, inland lakes, and Lake Michigan. Six species of crayfish were captured, including two invasive species. The invaders are the widely distributed and abundant Faxonius rusticus (rusty crayfish) and Procambarus clarkii (red Swamp crayfish), a species early in the invasion phase. Native species were found in fewer habitat types and were less abundant than invasive F. rusticus. Comparing our results to previous sampling showed that native crayfish distribution and diversity have declined at the same time that F. rusticus has spread over recent decades. There is potential for new and recently introduced invaders, such as the red swamp crayfish, to further alter ecosystems.

Using network ecology to understand and mitigate long‐term insect declines

Using network ecology to understand and mitigate long‐term insect declines

Synthesis of interannual variability in spatial demographic processes supports the strong influence of cold-pool extent on eastern Bering Sea walleye pollock (Gadus chalcogrammus)

Attributing variability in fish demographic processes to environmental conditions is helpful when assessing population status and forecasting changes in ecosystem function. Empirical orthogonal function (EOF) analysis has long been used to explore variability in physical processes, but has been only recently employed to study variability in biological processes. EOF analysis estimates dominant modes of variability (indices) and produces maps representing the spatial response for the dependent variable to each of these indices. In the eastern Bering Sea (EBS), research has linked demographic processes to the spatial extent of bottom temperatures less than or equal to 2 °C (the “cold-pool extent” or “CPE”), but has generally not compared effects among different demographic processes. We applied EOF analysis to four types of data measuring the outcome of demographic processes for EBS walleye pollock (Gadus chalcogrammus) over the period 1982–2019: numerical density (outcome of movement), morphometric condition (outcome of bioenergetics), length-at-age (outcome of growth), and prey-biomass-per-predator-mass (a proxy for stomach contents; outcome of consumption). We first designed exploratory factor analysis (EFA) models that did not include a CPE effect. We then applied confirmatory factor analysis (CFA), which differed from EFA by attributing observed patterns to a spatially varying response of demographic processes to CPE. We inferred that CPE was a proxy for demographic variability when there was a strong correlation between (1) the first or second mode of variability in the EFA and CPE or (2) the spatial map associated with the positive phase of the first or second mode of variability from the EFA model and the spatially varying response of CPE from the CFA model. Results showed that prey-biomass-per-predator-mass had the strongest correlation with CPE, numerical density and morphometric condition were also strongly correlated with CPE, and length-at-age was moderately correlated with CPE. The models also identified several anomalous years: 1999 and 2010, which were characterized by a very large CPE and high indices for variables related to demographic processes; and 2016–2019, which were characterized by a small CPE and low indices for variables related to demographic processes. We conclude that demographic processes for EBS walleye pollock show the finger-print of bottom-up environmental variation. Future research can employ CPE projections to forecast spatio-temporal changes in variables related to demographic processes, thereby informing estimates such as weight-at-age that are used in stock assessment models.

Human-driven changes in sediment-water interactions may increase the degradation of ecosystem functioning in the Ganga River

While it is widely accepted that the magnitude of river water quality degradation depends upon the proportion of human interventions, the overall changes are ultimately the consequence of interconnected biogeochemical processes with poorly understood role of ecosystem feedbacks. Here, we conducted in situ and incubation experiments, considering a 620 km Ganga River main stem, two tributaries and two point source downstream locations for trajectory studies to analyze the human-driven changes in ecosystem feedback associated changes in ecosystem functioning of the Ganga River and its tributaries. The main stem coupled trajectory analyses show that benthic hypoxia/anoxia resulting from intensive human releases generates positive feedbacks (sediment-P and –metal release) to exacerbate the degradation of ecosystem functioning in the Ganga River and tributaries. We found 1.9 to 4.6 times higher rates of sediment-P release and about 1.1 to 3.7 times higher rates of sediment-metal releases at sites with DOsw < 2.0 mg/L. Excess release of phosphorus from sediment enhanced the eutrophy whereas sediment-metal release and bioavailability led to a sharp decline in microbial biomass and FDAase activity. The Carlson’s index, ecological response index, Dodds’s trophic state classification, and risk index support these results because the sites with benthic hypoxic/anoxic condition did show trophic state in eutrophic to hypereutrophic range and metal pollution in very high to extremely polluted and high risk category indicating significant effect of these drivers. The study, for the first time, showed that positive feedbacks exacerbate the degradation of ecosystem functioning in human-impacted large rivers. We suggest the need for increased efforts considering the magnitude and connectivity of positive feedbacks and associated repercussions for improving mechanistic understanding of their contributions to overall structural and functional shifts in the large rivers.

Diverging land-use projections cause large variability in their impacts on ecosystems and related indicators for ecosystem services

Abstract. Land-use models and integrated assessment models provide scenarios of land-use and land-cover (LULC) changes following pathways or storylines related to different socioeconomic and environmental developments. The large diversity of available scenario projections leads to a recognizable variability in impacts on land ecosystems and the levels of services provided. We evaluated 16 projections of future LULC until 2040 that reflected different assumptions regarding socioeconomic demands and modeling protocols. By using these LULC projections in a state-of-the-art dynamic global vegetation model, we simulated their effect on selected ecosystem service indicators related to ecosystem productivity and carbon sequestration potential, agricultural production and the water cycle. We found that although a common trend for agricultural expansion exists across the scenarios, where and how particular LULC changes are realized differs widely across models and scenarios. They are linked to model-specific considerations of some demands over others and their respective translation into LULC changes and also reflect the simplified or missing representation of processes related to land dynamics or other influencing factors (e.g., trade, climate change). As a result, some scenarios show questionable and possibly unrealistic features in their LULC allocations, including highly regionalized LULC changes with rates of conversion that are contrary to or exceed rates observed in the past. Across the diverging LULC projections, we identified positive global trends of net primary productivity (+10.2 % ± 1.4 %), vegetation carbon (+9.2 % ± 4.1 %), crop production (+31.2 % ± 12.2 %) and water runoff (+9.3 % ± 1.7 %), and a negative trend of soil and litter carbon stocks (−0.5 % ± 0.4 %). The variability in ecosystem service indicators across scenarios was especially high for vegetation carbon stocks and crop production. Regionally, variability was highest in tropical forest regions, especially at current forest boundaries, because of intense and strongly diverging LULC change projections in combination with high vegetation productivity dampening or amplifying the effects of climatic change. Our results emphasize that information on future changes in ecosystem functioning and the related ecosystem service indicators should be seen in light of the variability originating from diverging projections of LULC. This is necessary to allow for adequate policy support towards sustainable transformations.