Ecological Response Variables Research Articles

Shoreline restoration including armor removal and log placement affect ecosystem recovery through time

The impacts of individual restoration activities, such as the total area covered and specific actions taken, can be difficult to measure because they are typically not performed randomly or independently. In Puget Sound, Washington, United States, removal of hard armor is a primary shoreline restoration measure. The length of armor removed from a beach and additional restoration actions implemented can vary considerably. As such, it is challenging to attribute specific ecological responses to particular actions. We use an extensive collection of sites regularly monitored pre‐ and post‐restoration to explore the success of different extents of armor removal and three supplemental “living shoreline” restoration actions: native vegetation planting, log placement, and sediment supplementation (“nourishment”). We measured five ecological response variables: sediments (percent surface, subsurface gravel), beach logs (count, line width), beach wrack (percent cover, depth), riparian vegetation (percent cover of supratidal, backshore), and supratidal invertebrates (density, richness). Only beach logs were affected by the length of armor removed, whereas wrack increased regardless of length. Invertebrate abundance increased through time only when supplemental vegetation planting did not occur. Placement of logs post armor removal was an impactful supplemental restoration strategy, positively affecting not only the further accumulation of logs, but also the amount of wrack and gravel sediments. Sediment nourishment only affected the proportion of subsurface gravel, which decreased through time in nourished sites. We stress the importance of the thorough monitoring of the ecological effects of living shoreline restoration actions to better understand their role in ecosystem recovery through time.

Coastal landforms and fetch influence shoreline restoration effectiveness

Coastal shorelines are a key interface between terrestrial and aquatic ecosystems and are vital for human livelihood. As a result, shorelines have experienced substantial human modifications worldwide. Shoreline “hardening” – the construction of armor including seawalls, bulkheads, or rip-rap – is a common modification that has substantial negative ecological effects. Currently, restoration involving the removal of armor and replacement with “living” shorelines is becoming an established practice. Still, the ecological response to armor removal is oftentimes unpredictable and site-specific. We hypothesized that the confluence of larger-scale geophysical features might strongly influence ecological restoration outcomes at particular locations. To measure the effectiveness of armor removal in the context of broad-scale geophysical features across the Salish Sea, WA, USA, we studied 26 paired restored and natural reference beaches of the same shoretype (feeder bluff, accretion shoreform, or pocket beach), as well as corresponding fetch, sub-basin, and percent of shoreline sediment drift cell armored. Sites were restored for an average of six years. We gauged restoration effectiveness based on levels of five ecological response variables: beach wrack (percent, depth), logs (count, width), sediments (percent sand), vegetation (percent overhanging, count of fallen trees), and insects (density, taxa richness). We found that armor removal often restored these variables to natural levels, but that restoration response was dependent on geophysical features such as shoretype and fetch. Natural beaches did have higher measurements of overhanging vegetation, fallen trees, and insect taxa richness, as these features likely take time to mature at restored beaches. Feeder bluffs had a higher proportion of surface sand and number of fallen trees than other shoretypes, coinciding with the erosion of bluff material, whereas natural pocket beaches within bordering rocky headlands had higher insect densities. Sites with a large fetch had higher input of deposited wrack and logs, whereas sites with a small fetch had higher input from localized terrestrial sources – fallen trees and eroding sand. By incorporating the effectiveness of restoration with landscape features such as shoretype and fetch, we can more effectively plan for future restoration actions and better predict their outcomes.

Digital and Geographical Feature Detection by Machine Learning Techniques Using Google Earth Engine for CPEC Traffic Management

The center of human settlements is in the cities, which must have high-quality habitats for their inhabitants. Many megachallenges of urbanization, population development, global advancement, environmental destruction, traffic management, and climate change must be addressed. This study is aimed at understanding how to maintain balanced land development in rapidly urbanizing towns to solve this challenge and mobility issues. Climate and weather forecasts, land cover, environmental indices, nonoptical and optical wavelengths, water history, and air quality are only some of the datasets available on Google Earth Engine, a publicly usable data repository. Machine learning techniques, i.e., random forest (RF), support vector machine (SVM), and classification and regression tree (CART), are used to monitor spatial-temporal change regarding water, vegetation, and urbanization for Pakistan from 2013 to 2021 using Landsat 8. The detection of urban land suitability concerning multiple metrics such as ecological response variables, environmental tension, socio-economic development potential, and natural resource potential is also found. Dataset features were classified as bands in the Google Earth Engine. Moreover, for 2020 and 2021, classification results showing the change in water, vegetation, and urbanization are also represented concerning China Pakistan Economic Corridor (CPEC) highway and the railway track to monitor and control traffic and its management.

A new index of resilience applicable to external pulse-disturbances that considers the recovery of communities in the short term

Resilience is a key concept in the study of the recovery of ecosystems affected by disturbances. Currently, there are numerous indices to measure resilience, but many of them do not show the accuracy of the resilience value or the behaviour of ecological parameters in the face of disturbances. New approaches and technologies enable large amounts of information to be obtained, facilitating the proposal of new resilience indices that work consistently and intuitively for a wide variety of ecological response variables under different scenarios after pulse-disturbances. In this study, we propose and verify a new resilience index, comparing its performance with others previously published. We validated the performance of the new index using real data based on field measurements of changes in soil bacterial OTUs diversity and abundance after a wildfire. The new resilience index provided an automatic and robust functional classification of the behaviour of ecosystems after disturbances, supported by a bootstrap analysis. We identified 5 scenarios of ecosystem resilience performance according to their behaviour after a pulse-disturbance: resilient, non-resilient, recovering, rebound, and continuing.

Meta-analysis on a Decade of Testing Corridor Efficacy: What New Have we Learned?

Corridors are widely considered as a strategy to mitigate effects of habitat fragmentation on biodiversity. There are, however, lingering concerns about whether corridors work as intended and whether managing for connectivity in fragmented landscapes is even important for biodiversity conservation. In response, numerous manipulative and natural experiments have been conducted to test the effectiveness of corridors. Gilbert-Norton et al. Conserv Biol. 2010;24(3):660-8 (2010) reviewed such studies published between 1985 and 2008 and concluded that corridors are generally effective at increasing inter-patch movement. The authors noted a lack of studies measuring responses at the population and community levels, responses that would better approximate corridor effects on population persistence and aspects of biodiversity. Here I explored what new insights can be gained on corridor effectiveness from studies published in the last decade, particularly with an eye toward insights going beyond effects on inter-patch movement. Following the same selection criteria as Gilbert-Norton et al. Conserv Biol. 2010;24(3):660-8 (2010), I reviewed studies published between 2008 and 2018 that tested corridor effectiveness by comparing ecological response variables from patches connected and not connected by corridors. Analysis of effect sizes showed that corridors increase response variables, reinforcing earlier conclusions that corridors function as intended. Whereas the previous review mainly included corridor effects on dispersal, recent research shows support for corridor efficacy at a variety of levels of organization, from individuals to communities. These findings provide further support for the conclusion that efforts spent creating and maintaining corridors are worthwhile for biodiversity conservation.

Genetic and environmental contributions to the impact of a range-expanding predator on aquatic ecosystems.

Global change is altering biodiversity locally and globally and subsequently affecting the dynamics of communities and ecosystems. Biodiversity can be impacted both at the interspecific (i.e., species composition of communities) and at the intraspecific (evolutionary modification of phenotypic traits through selection or plasticity) levels. Changes in intraspecific diversity have been demonstrated to generate evolutionary feedbacks acting on ecological dynamics. Quantifying the role of intraspecific trait variation, global change and their interactions on ecological dynamics is of utmost importance. Here, we used the range-expanding dragonfly Crocothemis erythraea as a model species to test the relative effects of intraspecific trait variation in larvae and thermal conditions on the dynamics of freshwater community and ecosystem functioning. Using experimental mesocosms, we manipulated intraspecific trait variation arising from genetic (G), early developmental environment (EE ) and late developmental environment (EL ) contributions in a full factorial design. We showed that intraspecific trait variation arising from genetic effects has the strongest consequences on community and ecosystem dynamics relative to trait variation driven by the thermal environment (EE and EL ). Importantly, the ecological effects of trait variation due to genetic effects were partly modulated by thermal conditions (G×EL , and to a lesser extent G×EE interactions) and varied among ecological response variables. For instance, the strongest G×EL effects were observed on primary productivity and zooplankton dynamics. Trait variation driven by plasticity related to early or late developmental environments has an overall weak effect on ecological dynamics. Intraspecific trait variation induced by genetic effects can affect ecological dynamics (evo-to-eco dynamics) more strongly than variation induced by the developmental environment. However, they likely interact to modulate the structure of communities and the functioning of ecosystems, highlighting the strong context (environmental) dependency of evo-to-eco dynamics.

Additive effects prevail: The response of biota to multiple stressors in an intensively monitored watershed

Freshwater ecosystems are impacted by a range of stressors arising from diverse human-caused land and water uses. Identifying the relative importance of single stressors and understanding how multiple stressors interact and jointly affect biology is crucial for River Basin Management.This study addressed multiple human-induced stressors and their effects on the aquatic flora and fauna based on data from standard WFD monitoring schemes. For altogether 1095 sites within a mountainous catchment, we used 12 stressor variables covering three different stressor groups: riparian land use, physical habitat quality and nutrient enrichment. Twenty-one biological metrics calculated from taxa lists of three organism groups (fish, benthic invertebrates and aquatic macrophytes) served as response variables. Stressor and response variables were subjected to Boosted Regression Tree (BRT) analysis to identify stressor hierarchy and stressor interactions and subsequently to Generalised Linear Regression Modelling (GLM) to quantify the stressors standardised effect size.Our results show that riverine habitat degradation was the dominant stressor group for the river fauna, notably the bed physical habitat structure. Overall, the explained variation in benthic invertebrate metrics was higher than it was in fish and macrophyte metrics. In particular, general integrative (aggregate) metrics such as % Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa performed better than ecological traits (e.g. % feeding types). Overall, additive stressor effects dominated, while significant and meaningful stressor interactions were generally rare and weak.We concluded that given the type of stressor and ecological response variables addressed in this study, river basin managers do not need to bother much about complex stressor interactions, but can focus on the prevailing stressors according to the hierarchy identified.

A Bayesian approach for temporally scaling climate for modeling ecological systems.

With climate change becoming more of concern, many ecologists are including climate variables in their system and statistical models. The Standardized Precipitation Evapotranspiration Index (SPEI) is a drought index that has potential advantages in modeling ecological response variables, including a flexible computation of the index over different timescales. However, little development has been made in terms of the choice of timescale for SPEI. We developed a Bayesian modeling approach for estimating the timescale for SPEI and demonstrated its use in modeling wetland hydrologic dynamics in two different eras (i.e., historical [pre‐1970] and contemporary [post‐2003]). Our goal was to determine whether differences in climate between the two eras could explain changes in the amount of water in wetlands. Our results showed that wetland water surface areas tended to be larger in wetter conditions, but also changed less in response to climate fluctuations in the contemporary era. We also found that the average timescale parameter was greater in the historical period, compared with the contemporary period. We were not able to determine whether this shift in timescale was due to a change in the timing of wet–dry periods or whether it was due to changes in the way wetlands responded to climate. Our results suggest that perhaps some interaction between climate and hydrologic response may be at work, and further analysis is needed to determine which has a stronger influence. Despite this, we suggest that our modeling approach enabled us to estimate the relevant timescale for SPEI and make inferences from those estimates. Likewise, our approach provides a mechanism for using prior information with future data to assess whether these patterns may continue over time. We suggest that ecologists consider using temporally scalable climate indices in conjunction with Bayesian analysis for assessing the role of climate in ecological systems.

A hydrologically sensitive invertebrate community index for New Zealand rivers

Identifying ecological response variables sensitive to hydrological change is a key step in determining the impacts of river flow alterations on aquatic ecosystems and in setting environmental flows that sustain certain ecological values. Building on the successful use of flow regime sensitive aquatic invertebrate indices in other countries, particularly the UK based Lotic Index for Flow Evaluation (LIFE), we provide two variants of a similar index for use in New Zealand (LIFENZ and a weighted variant: LIFENZ_W). As in the original LIFE, the New Zealand indices were based on water velocity preference categories assigned to aquatic invertebrate taxa using professional judgement. To calculate the indices a lookup table is used to assign a score to each taxon based on their velocity category and abundance. For the LIFENZ_W variant an additional step down weighted the scores if the taxon has a general compared to a more specific velocity preference. The two index variants were correlated with each other and to similar environmental parameters. Across a total of 74 sites, both indices were correlated with depth-averaged water velocity. Changes in index values, both between sites and temporally within sites, were predominantly associated with changes in hydrological parameters, such as the magnitude and length of time since a recent high flow, and to a lesser degree with other physico-chemical parameters. Commonly used indices in New Zealand designed to respond to nutrient enrichment (MCI and variants) were not correlated with local water velocity, but were correlated with antecedent flow conditions and were likely influenced by effects of flow stability on algal growth. Further testing of LIFENZ and LIFENZ_W in combination with MCI is recommended, particularly in rivers subject to more extreme hydrological and water quality stresses and with regard to other physical parameters such as hydraulic habitat. However, the LIFENZ and its weighted variant (LIFENZ_W) appear to be useful tools for understanding and managing the effects of hydrological alteration on aquatic invertebrate communities in New Zealand. As LIFENZ and LIFENZ_W were strongly correlated and only showed a relatively small deviation from a slope of 1 we recommend the use of the more straightforward LIFENZ in almost all circumstances.

How do low magnitudes of hydrologic alteration impact riverine fish populations and assemblage characteristics?

Water managers need quantitative information on the effects of hydrologic alteration on aquatic biota to guide ecologically sensitive water management strategies such as water releases from dams. A key gap in the global research literature is determining whether low levels of hydrologic alteration have significant effects on fish populations and assemblage characteristics. This study quantified patterns of fish response to flow regime alteration in a sub-tropical region where many rivers have regulated flow regimes but 57% of ecologically relevant flow metrics have changed by <20%. We tested for flow regulation effects on 17 (univariate and multivariate) response variables representing fish population abundance and assemblage characteristics using a field design based on the environmental flow assessment framework known as ELOHA (Ecological Limits of Hydrologic Alteration). Ecological response variables that are readily quantified and sensitive to variation and alteration in flow regimes are critical to the application of environmental flow frameworks such as ELOHA. In this study only three of 17 response variables representing fish population abundance and assemblage attributes showed significant differences between regulated and unregulated reaches (densities of both Pseudomugil signifier and Melanotaenia duboulayi, and fish assemblage composition). Effects associated with flow regulation were most evident where historically intermittent flow regimes have become more perennial as a consequence of managed water releases from dams. Our study provides positive evidence that dams and regulated flow regimes can be managed with sensitivity such that there are few significant changes in populations of most fish species, and little change in fish assemblage characteristics. However, it must be cautioned that the magnitude of flow regime alteration may interact with the duration of exposure (i.e. years to decades) such that other ecological impacts emerge over time as species and assemblages adjust to altered flow regimes.

A test of The Ecological Limits of Hydrologic Alteration (ELOHA) method for determining environmental flows in the Potomac River basin, U.S.A.

Summary The Ecological Limits of Hydrologic Alteration (ELOHA) method described in Poff et al. (2010) was applied to streams and small rivers in a large central region of the Potomac River basin in the U.S.A. The area, which is topographically complex, has karst geology, is increasingly urban and has few flow‐altering impoundments, allows a test of the flexibility and applicability of the ELOHA method's four steps: build a hydrological foundation, calculate flow alteration, classify streams and develop flow alteration–ecology (FA‐E) relationships. A hydrological foundation of baseline (undisturbed) and current (existing) hydrographs was simulated for 747 catchments using the Chesapeake Bay Program Hydrologic Simulation Program‐FORTRAN (HSPF) model and the Virginia Department of Environmental Quality Online Object Oriented Meta‐Model (WOOOMM) routing module. The outlet of each catchment was associated with one, and sometimes two or more, stream macroinvertebrate sampling sites. Pairing each catchment's simulated current flow with its own simulated baseline flow produced estimates of flow alteration that reflect the combination of natural and anthropogenic factors controlling streamflow in individual catchments. Flow metrics from the baseline and current simulations were compared with observed values from gauged streams in undisturbed and disturbed catchments. The model may have failed to simulate streamflow well in small urbanised catchments on or near karst geology, but observed data were insufficient to fully evaluate model behaviour in these units. Elsewhere, simulated and observed values of 13 of the 15 tested flow metrics generally agreed well. A stream hydrological classification system to account for natural biological variability was not feasible in the study area for two reasons. First, the natural landscape features that most strongly govern undisturbed streamflows (catchment size and karst geology) do not greatly influence undisturbed macroinvertebrate communities. Second, the study area's complex topography ensures that many streams crossed physiographic boundaries or flowed through karst geology before reaching the macroinvertebrate sampling sites. Stream macroinvertebrates responded strongly to alteration in the duration and frequency of both high and low flow events, rise rate, flashiness and magnitude of high flow events. They did not respond to the alteration in middle‐ and low‐magnitude flow metrics, fall rate or extreme low flow frequency. Flow alteration–ecological relationships were developed for combinations of six flow metrics and seven macroinvertebrate metrics using quantile regression and conditional probability methods. Of the seven macroinvertebrate metrics, % scrapers, % clingers and the Chessie BIBI were most affected by flow alteration. Degraded habitat and water quality conditions modify and, if strong enough, conceal the flow alteration–ecological relationships. Water quality and habitat improvements can potentially ameliorate the impacts of flow alteration. Resource managers need to view each stream system holistically and consider all anthropogenic stressors before the impact of existing or future flow alteration can be determined. Overall, the ELOHA approach appears to have worked well in a large river basin with complex topography, karst geology, few flow‐altering dams, many urban areas and macroinvertebrates as the ecological response variables.

Performance of Drought Indices for Ecological, Agricultural, and Hydrological Applications

Abstract In this study, the authors provide a global assessment of the performance of different drought indices for monitoring drought impacts on several hydrological, agricultural, and ecological response variables. For this purpose, they compare the performance of several drought indices [the standardized precipitation index (SPI); four versions of the Palmer drought severity index (PDSI); and the standardized precipitation evapotranspiration index (SPEI)] to predict changes in streamflow, soil moisture, forest growth, and crop yield. The authors found a superior capability of the SPEI and the SPI drought indices, which are calculated on different time scales than the Palmer indices to capture the drought impacts on the aforementioned hydrological, agricultural, and ecological variables. They detected small differences in the comparative performance of the SPI and the SPEI indices, but the SPEI was the drought index that best captured the responses of the assessed variables to drought in summer, the season in which more drought-related impacts are recorded and in which drought monitoring is critical. Hence, the SPEI shows improved capability to identify drought impacts as compared with the SPI. In conclusion, it seems reasonable to recommend the use of the SPEI if the responses of the variables of interest to drought are not known a priori.

Linking Geomorphological and Ecological Responses in Restored Urban Pool-Riffle Streams

Anne Chin, Frances Gelwick, David Laurencio, Laura R. Laurencio, Morgan S. Byars and Mateo Scoggins

Responses of stream macroinvertebrates and ecosystem function to conventional, integrated and organic farming

Summary 1. Organic farming practices can benefit a wide range of terrestrial biota in comparison to conventional farming but we do not know whether this benefit extends to streams flowing through farmed landscapes. 2. We measured the impacts of organic, integrated management and conventional farming on the taxonomic and trait composition of macroinvertebrate communities and on stream ecosystem functioning (algal accrual on tiles and leaf breakdown). Our study design included five replicates of each farming practice, arranged in blocks, in agricultural land dedicated to the farming of sheep and beef cattle on pasture in southern New Zealand. In each farm stream, we studied both upstream and downstream reaches within the farm’s boundaries. 3. The different farming practices were reflected in contrasting stream physicochemistry (total dissolved nitrogen, fine sediment on the bed and glyphosate concentrations in the bed sediment) and in differences in both the taxonomic organization and trait representation of stream invertebrate communities. Conventional farm streams showed the strongest negative responses, whilst the condition of organic and integrated farm streams was similar. 4. Invertebrate trait measures proved as effective as taxonomic measures in their response to agricultural intensity, whereas ecosystem function measures were least sensitive. 5. There were no overall physicochemical differences between upstream and downstream sites within the farms and few notable longitudinal patterns in ecological response variables. 6. Synthesis and applications. Conventional farming had the strongest adverse consequences for stream condition in our study. In contrast, an integrated management system (aimed at reducing pesticide use, increasing beneficial pest predators and encouraging environmentally responsible soil, water and energy management) proved at least as effective as organic farming and, together with organic farming, can be considered better practice.

IMPACT OF WEATHER ON A LAKE ECOSYSTEM, ASSESSED BY CYCLO-STATIONARY MCCA OF LONG-TERM OBSERVATIONS

Temperate lake ecosystems are generally characterized by a strong annual cycle, and the relationships between observations of such ecosystems and external forcing variables can exhibit a complex structure. Furthermore, the observational data record is often short. This makes it difficult to assess the relationships between external forcing factors and their impact on the biological succession. Cyclo-stationary maximum cross-covariance analysis (MCCA) allows the effects of seasonality to be modeled in a flexible way, and we describe this statistical technique in detail. MCCA offers an objective method to approximate the high-dimensional total cross-covariance structure by defining “weighting” patterns. With a predictor set of reduced dimension, a suitable regression between forcing variables and ecological response variables can be set up. Cyclo-stationary MCCA is used here to analyze the influence of meteorological variables (air temperature, wind speed, global radiation, humidity, and precipitation) on 13 biological and biogeochemical indicator variables of Plußsee, a small lake in northern Germany. The main weather influence on the indicator variables was found to be connected to winter temperature. From the covariance structure the following major signals were detected to be related to higher winter temperature: a more intense spring algal maximum, a higher zooplankton biomass during the algal maximum, a less intense loss of nutrients to the hypolimnion, a higher summer bloom together with changes in the nutrient concentrations, and stronger oxygen consumption in autumn.