Determining Reference Conditions Research Articles

Nonnative invasive species are overlooked in biological integrity assessments

Multimetric indices (MMIs) are common tools used to assess the biological status of ecosystems. However, not all the components of biological integrity have been equally addressed, since most of MMIs do not consider nonnative species, which are a great threat to ecosystems integrity. We performed a systematic review of how nonnative species have been considered in MMIs to assess biological conditions worldwide. Using a systematic review of the literature we identified to what extent nonnative species have been included as a disturbance factor for determining reference conditions and if specific metrics related to both nonnative and native species have been taken into account in the MMIs around the world. We also identified the most frequent species origin metrics that have been included in the MMIs. We searched for articles published in English up to 2016 that applied or developed an MMI in the Web of Science database (Clarivate Analytics). Following the PRISMA guidelines, we analyzed 409 articles. We found that only 1.2% of the studies used nonnative species as a disturbance factor in determining reference conditions. About 66% of articles did not test or did not provide the information if they tested metrics on native or nonnative species. Most of the articles (53%) that tested native or nonnative metrics were fish-based MMIs. We found 97 different metrics, of which 69% were related to native species, whereas 31% were related to nonnative ones. Native richness was the most used metric in studies that considered species origin (23.5%). Our main results evidence that nonnative species are overlooked in biomonitoring programs. Owing to the well-known impacts of them on ecosystem integrity, their inclusion in definition of reference conditions and in MMIs metrics should be considered as bioassessment criteria.

Climatic and structural comparison of yellow pine and mixed-conifer forests in northern Baja California (México) and the eastern Sierra Nevada (California, USA)

Effects of fire suppression policies on semi-arid yellow pine and mixed conifer (YPMC) forests in the western US have been well documented, and restoration of forest structure and natural fire regimes are high management priorities to ensure the health and resilience of such forests. However, determining reference conditions for ecological restoration is difficult due to the near absence of undegraded forests in the US. YPMC forests of the Sierra de San Pedro Mártir (SSPM) in northern Baja California, Mexico, are highly similar to forests of the Eastern Sierra Nevada, California, USA, have experienced little to no logging, and until relatively recently supported a natural fire regime. As such, these Mexican YPMC forests are thought by many to represent reference ecosystems for restoration and resource and fire management in the US. However, to this point there has been no direct climatic comparison to determine to what extent SSPM is validly compared to California YPMC sites, nor a direct statistical comparison of forest conditions to see in what ways northern California forests might differ from SSPM. We compared climatic data from SSPM with 17 meteorological stations in the range of Jeffrey pine in Alta and Baja California. Based on this comparison, we determine that SSPM clearly belongs to the general class of Jeffrey pine-dominated YPMC forests found along the eastern edge of the California Floristic Province. We used field sampling to measure forest structure, fuels, and vegetation and ground cover in SSPM and in multiple National Forests along the eastern slope of the Sierra Nevada. Live tree density was nearly twice as high in the eastern Sierra Nevada as in SSPM, and dead tree density was 2.6 times higher. Basal area was about 30% higher in the eastern Sierra Nevada, even though average tree size was larger in SSPM. Fuel loads and coarse woody debris were very similar between the two sites, and fine fuels (1-hour fuels) were actually higher in SSPM. Logging and fire suppression have resulted in denser YPMC forests dominated by smaller trees in the US, but our results suggest that fire suppression in SSPM over the last 30years has increased fuel loads. Nonetheless, the Baja California forests still retain an overstory structure created and maintained by centuries of frequent fire. This study provides important reference information for the management of eastern Sierra Nevada forests, and indicates that continued full fire suppression in SSPM carries significant ecological risks.

Responses of Aquatic Ecosystems to Environmental Changes in Finland and China

The concern for the state of global freshwater reservoirs has increased due to deterioration of the water quality during the last decades. This has prompted monitoring and restoration efforts such as the European Water Framework Directive and the national-scale 2nd-investigation and monitoring of the water quality, water volume and biota resources in China. The challenge so far has been the determination of the “natural” state (reference conditions) of freshwater ecosystems. We used the sediment archives of five lakes and one brackish water embayment in Finland and China to assess the impact of selected variables of climatology, hydrology, nutrients, and changes in human population on these ecosystems during the last few centuries. The study sites represent catchment areas with varying land use. Despite the long distance between the sites and their different land-use characteristics, the direction and timing of changes during the last few centuries are well comparable between the high latitudes of Finland and the mid-low latitudes of China. This study reinforces the sensitivity of aquatic ecosystems to environmental change and underlines the usefulness of the palaeolimnological approach as a tool for determining reference conditions.

Using SWAT to determine reference nutrient conditions for small and large streams

Developing reference criteria for nutrient conditions on streams can be difficult especially in heavily farmed or urbanized regions where most of the landscape has been impacted by human development. SWAT (soil water assessment tool) simulations permit the removal of the anthropogenic impacted land use, allowing the simulation of natural conditions and a prediction of reference conditions. A Genesee River watershed simulation was developed to determine the nutrient and sediment contributions of subbasins of the Genesee River under the current human-impacted conditions and contrasted against natural conditions. Nutrient boundary values estimated for Genesee basin small wadeable streams (34.3μgP/L) were nearly identical to those calculated by others for small, wadeable streams (30.7μgP/L). For large streams, the simulation-based boundary total phosphorus (TP) value (75.8μgP/L) of the Genesee River was high compared to other observations in New York State (30μgP/L). Causes in the variability in large stream reference values include inappropriate use of regional reference conditions, stream bank erosion, basin geology, soil type, and catchment area. When river bank stabilization was added to the simulation, a 34.3% reduction in phosphorus loading was observed, resulting in a boundary value of ~54μgP/L. This reduction in the simulated sediment load suggested that the Genesee River has a higher natural sediment and TP load than most streams in NYS. SWAT is an effective tool for simulations of small streams and may be an effective method in determining reference conditions for large rivers.

Determining reference conditions for TN, TP, SD and Chl-a in eastern plain ecoregion lakes, China

Establishing the nutrient reference condition (baseline environmental condition) of lakes in an ecoregion is a critical consideration in the development of scientifically defensible aquatic nutrient criteria. Three methods were applied to determine reference conditions in the Eastern plain ecoregion lakes with respect to total phosphorus (TP), total nitrogen (TN), planktonic chlorophyll a (Chl-a) and Secchi depth (SD). The reference condition value for the lakes in the Eastern plain ecoregion by the trisection method is TP of 0.029 mg/L, TN of 0.67 mg/L, Chl-a of 3.92 mg/m3, SD of 0.85 m, and the reference condition range by the lake population distribution approach is TP of 0.014–0.043 mg/L, TN of 0.360–0.785 mg/L, Chl-a of 1.78–4.73 mg/m3, SD of 0.68–1.21 m. Additionally, empirical models were developed for estimating the reference Chl-a concentration and SD successfully for lakes in the Eastern plain ecoregion. Overall, the data suggest that multiple methods can be used to determine reference conditions and that in Eastern plain ecoregion lakes the reference condition corresponds to a mesotrophic status.

Determining reference conditions for nutrients, chlorophyll a and Secchi depth in Yungui Plateau ecoregion lakes, China

AbstractEstablishing nutrient reference condition (baseline environmental condition) of lakes in ecoregion is a critical consideration in the development of scientifically defensible aquatic nutrient criteria. Three methods were applied to determine reference conditions in Yungui Plateau ecoregion lakes with respect to total phosphorus, total nitrogen, planktonic chlorophyll a (chl a) and Secchi depth. First, minimally developed lake/catchment units were identified based on existing geographical database and visual basin survey. Lakes in these catchments were considered minimally disturbed ‘reference lakes’. Second, the frequency distribution of all of the lake data presently available by each variable was plotted, and the lower 25th percentile was selected as the reference condition for each value. Third, median nutrient, chl a and Secchi depth values were determined for the best one‐third of lakes and applied as indicators of reference condition. The result of model prediction and data from historical record were used to test three techniques for determining reference condition. Reference conditions, as determined by these three methods, broadly agreed for all parameters. Overall, the data suggest that multiple methods can be used to determine reference condition, and that in Yungui lakes, reference condition corresponds to oligotrophic–mesotrophic status.

Defining ecological and chemical reference conditions and restoration targets for nine European lakes

This paper aims to determine the ecological and chemical reference conditions (~1800–1850 AD) and degree of floristic change at nine enriched lakes, covering a range of types across Europe, using fossil diatom assemblages in dated sediment cores and application of total phosphorus (TP) transfer functions. Additionally the study assesses the potential of analogue matching as a technique for identifying reference sites and for estimating reference TP concentrations for the study lakes using a training set of 347 European lakes and 719 diatom taxa. Oligotrophic, acidophilous to circumneutral taxa were predominant in the reference samples of several of the deep lakes, and benthic Fragilaria spp. dominated the reference samples of two high alkalinity shallow lakes. The degree of floristic change from the reference sample, assessed using the squared chord distance (SCD) dissimilarity coefficient, revealed that two sites had experienced slight change (Lago Maggiore, Felbrigg Lake), five experienced moderate change (Mjoesa, Loch Davan, Loch Leven, White Lough, Esthwaite Water), and two showed evidence of major change (Groby Pool, Piburger See). For three lakes, there were no analogues in the diatom dataset owing to the uniqueness and diversity of the diatom reference assemblages. For the remaining six sites the number of analogues ranged from 2 to 44. For two deep lakes most of the analogues seemed appropriate as they were of the same type and had low TP concentrations. However, for two other deep lakes and two shallow lakes some of the analogues differed markedly in their depth and alkalinity from the lake in question or had TP concentrations seemingly too high to represent reference conditions suggesting that the analogues may not be suitable as reference sites. For the deep lakes, similar reference TP values were calculated using the EDDI Combined TP transfer function and the analogue matching technique with concentrations typically <20 μg L−1. However, for the shallow lakes, the analogue matching method produced inferred values considerably higher than those of the transfer function. The wide ecological tolerances of many of the diatom taxa found in the reference samples most likely explain the selection of inappropriate analogue sites. In summary, the study demonstrates that palaeoecological techniques can play a valuable role in determining reference conditions and indicates that the analogue matching technique has the potential to be a useful tool for identifying appropriate reference sites for lakes impacted by eutrophication.

Palaeolimnology and its developing role in assessing the history and extent of human impact on lake ecosystems

This Special Issue was produced as an output from the EU Integrated Project Euro-limpacs which aimed to evaluate the impacts of global change on European freshwater ecosystems using a combination of approaches, including monitoring, experiments, modelling and palaeolimnology. The papers focus on the last of these approaches. They examine the role of lake sediment records in determining reference conditions for a range of environmental pressures including acidification, eutrophication, metal pollution, organic carbon and sediment accumulation rates. The findings are especially relevant to the European Union’s Water Framework Directive which requires an assessment of lake ecological status based on deviation from reference conditions. The contributions consider a range of issues relating to the use of palaeolimnological data in defining reference conditions and lake status including human versus natural variability, concepts of pristine and reference conditions, shifting baselines, and quantification of degree of change. This introductory paper sets the context for the volume by briefly describing how palaeolimnology has evolved as a science, able now to contribute uniquely to the understanding of lake ecosystem change, especially with respect to the role of human activity over recent decades and centuries.

Drainage ditching at the catchment scale affects water quality and macrophyte occurrence in Swedish lakes

Summary1. We have limited knowledge of the effects of land use in general and of drainage ditching in particular on macrophyte communities in lakes. I quantified catchment land use, including drainage ditching, as well as water quality and the number of macrophyte species in 17 Swedish lakes in summer 2005.2. Land use within 1 km of the studied lakes was analysed in a geographic information system. The following variables were included: areas of forests, mires, agricultural land and urbanization, length of drainage ditches (classified according to the use of the land they drained), and shortest distance from lake to an urban area. To extract and analyse general trends in the data sets, redundancy analysis was used.3. Water quality was explained mainly by three land‐use related variables: the lengths of agricultural, forest and mire ditches. The length of agricultural ditches was positively correlated with lake water conductivity, total dissolved solids, Ca, N and total organic carbon (TOC). The lengths of forest and mire ditches were positively correlated with lake water characteristics, especially TOC.4. The number of species representing different macrophyte life forms was explained by three environmental variables: conductivity, and lengths of forest and agricultural ditches. The numbers of isoetids, nymphaeids, elodeids and total obligate hydrophytes were negatively correlated with length of forest ditches. In contrast, the number of lemnids and helophytes was positively correlated with conductivity and length of agricultural ditches. Furthermore, the number of isoetids was exponentially related (negatively) to lengths of agricultural and forest ditches, indicating a threshold response to drainage ditch length.5. The results suggest that effects on water quality and macrophyte communities result from drainage ditching in the lake catchments rather than from land use itself. Given the total area of drainage‐ditched land worldwide (millions of ha in Scandinavia alone), drainage ditching should be considered when evaluating environmental impacts on lake water quality and macrophyte occurrence and when determining reference conditions for catchment land use.

A bioassessment approach for mid-continent great rivers: the Upper Mississippi, Missouri, and Ohio (USA)

The objectives of the Environmental Monitoring and Assessment Program for Great River Ecosystems (EMAP-GRE) are to (1) develop and demonstrate, in collaboration with states, an assessment program yielding spatially unbiased estimates of the condition of mid-continent great rivers; (2) evaluate environmental indicators for assessing great rivers; and (3) assess the current condition of selected great river resources. The purpose of this paper is to describe EMAP-GRE using examples based on data collected in 2004-2006 with emphasis on an approach to determining reference conditions. EMAP-GRE includes the Upper Mississippi River, the Missouri River, and the Ohio River. Indicators include biotic assemblages (fish, macroinvertebrates, plankton, algae), water chemistry, and aquatic and riparian physical habitat. Reference strata (river reaches for which a single reference expectation is appropriate) were determined by ordination of the fish assemblage and examination of spatial variation in environmental variables. Least disturbed condition of fish assemblages for reference strata was determined by empirical modeling in which we related fish assemblage metrics to a multimetric stressor gradient. We inferred least disturbed condition from the y-intercept, the predicted condition when stress was least. Thresholds for dividing the resource into management-relevant condition classes for biotic indicators were derived using predicted least disturbed condition to set the upper bound on the least disturbed condition class. Also discussed are the outputs of EMAP-GRE, including the assessment document, multimetric indices of condition, and unbiased data supporting state and tribal Clean Water Act reporting, adaptive management, and river restoration.

Determining reference conditions for management and restoration of temperate grassy woodlands: relationships among trees, topsoils and understorey flora in little-grazed remnants

Temperate grassy woodlands were once widespread and dominant in many agricultural regions of south-eastern Australia. Most are now highly degraded and fragmented and exist within a context of broadscale landscape degradation. Greater understanding of natural processes in these woodlands is needed to benchmark management and restoration efforts that are now critical for their ongoing survival. We studied physical and chemical properties of topsoils from rare, little-grazed remnants of grassy Eucalyptus albens Benth. and E. melliodora Cunn. ex Schauer woodlands in central New South Wales and examined natural patterns in topsoil properties and understorey flora in relation to trees and canopy gaps. Topsoils were generally low in available macronutrients (nitrogen, phosphorus and sulfur), but were favourable for plant growth in most other measured characteristics. Topsoils beneath trees were notably more fertile than in open areas, particularly in total carbon, total nitrogen, available phosphorus, available potassium and salinity. Higher nutrient concentrations, particularly of available phosphorus, may have contributed to patterns in understorey dominants, with Themeda australis (R.Br.) Stapf predominating in open areas and Poa sieberiana Spreng. beneath trees. Trees were also associated with a higher native-plant richness, possibly resulting from their influence on the competitive dynamics of the dominant grasses. We discuss the implications of these interactions for the use of burning, grazing and slashing in woodland management and re-establishment of native grasses and trees in restoration efforts.

REFERENCE CONDITIONS FOR GIANT SEQUOIA FOREST RESTORATION: STRUCTURE, PROCESS, AND PRECISION

National Park Service policy directs that more natural conditions be restored to giant sequoia groves, which have been altered by a century of fire exclusion. Efforts to find a reasonable and practical definition of “natural” have helped drive scientists and land managers to use past grove conditions as reference conditions for restoration. Extensive research aimed at determining reference conditions has demonstrated that past fire regimes can be characterized with greater precision than past grove structures. Difficulty and imprecision in determining past grove structure has helped fuel a debate between “structural restorationists,” who believe that forest structure should be restored mechanically before fire is reintroduced, and “process restorationists,” who believe that simple reintroduction of fire is appropriate. I evaluate old and new studies from sequoia groves to show that some of the arguments of both groups have been flawed. Importantly, it appears that restoration of fire without a preceding mechanical restoration may restore the pre-Euro-American structure of sequoia groves, at least within the bounds of our imprecise knowledge of past grove structure. However, the same may not be true for all forest types that have experienced lengthy fire exclusion. Our ability to draw robust generalizations about fire's role in forest restoration will depend heavily on a thorough understanding of past and present interactions among climate, fire, and forest structure. Use of reference conditions will be central to developing this understanding.

Determining Reference Conditions for Ecosystem Management of Southwestern Ponderosa Pine Forests

Determining Reference Conditions for Ecosystem Management of Southwestern Ponderosa Pine Forests