Macrophyte Abundance Research Articles

Contrasting Effects of Increasing Invasive Crayfish Densities on Competing Submerged Macrophytes in Shallow Lakes

ABSTRACT Non‐native crayfish are among the most widespread aquatic invasive species worldwide. High densities of crayfish in lakes can potentially cause complete loss of macrophytes through herbivory, physical destruction, shading by suspension of sediments and nutrient release facilitating phytoplankton, thus altering ecosystem state and functions. However, lower crayfish densities may affect different macrophyte species in different ways, thus altering competition between macrophyte species with different growth forms. We hypothesize that high crayfish densities can completely destroy submerged macrophyte communities and shift systems into more turbid conditions whereas low crayfish densities can promote low‐growing macrophytes that compete with canopy‐forming species. To test these hypotheses, we applied three different densities (2, 4, 8 crayfish m−2) of the invasive crayfish Procambarus clarkii and a control (no crayfish) to 36 mesocosms of monocultures and mixed stands of low‐growing and canopy‐forming submerged macrophytes for 60 days. We measured concentrations of nutrients, suspended solids, phytoplankton and periphyton and above‐ and belowground biomass of low‐growing Vallisneria natans and canopy‐forming Hydrilla verticillata. In addition, we conducted a meta‐analysis of crayfish impacts on macrophytes to compare effect sizes between different crayfish densities. Using data from published studies, we derived the relationship between crayfish density and crayfish‐induced reductions in macrophyte abundance. Our meta‐analysis revealed a significant decline of macrophytes with increasing crayfish densities. In line with existing studies, high crayfish densities caused a strong loss of both low‐growing and canopy‐forming macrophytes and increased nutrient concentrations, phytoplankton biomass and suspended sediment, thus favouring an ecosystem shift to more turbid conditions. Low and medium crayfish densities reduced macrophyte biomass similarly for both species in monocultures. However, in mixed cultures, low crayfish densities (2 crayfish m−2) reduced the above‐ and belowground biomass of the canopy‐forming H. verticillata more than that of low‐growing V. natans, supporting our hypothesis. This support of low‐growing macrophytes occurred despite a temporal facilitation of shading by increased periphyton biomass. Our results show that the impact of crayfish invasions on aquatic ecosystems is strongly dependent on their density. High densities facilitate the loss of macrophytes and increase the likelihood of ecosystem collapse into a turbid state. However, low densities can provide a competitive advantage to low‐growing macrophytes that would otherwise be outcompeted by canopy‐forming species. Although complete eradication is often impossible, management of invasive crayfish can target densities that have potentially positive effects on invaded ecosystems.

Abundance, diversity and distribution of Macrophytes in lotic wetlands: A case study on Sironga and Kapkatet Wetlands, Kenya

Wetland macrophytes provide important ecological and social-economic values. However, the recent increase in anthropogenic influences has compromised the ecological integrity of most lotic wetlands, which has ultimately threatened their structure and functioning, causing degradation and loss of macrophytes. This study was aimed at assessing the biodiversity, distribution and abundance of macrophytes in Sironga and Kapkatet wetlands with respect to various anthropogenic activities. Sampling was conducted for a period of six months, covering both dry and wet seasons from February – July 2019. Macrophytes were identified using identification keys and diversity indices such as the Shannon-Wiener, Simpson’s, and Species evenness were used to determine macrophyte diversities. The numbers of different macrophytes species was enumerated from five randomly sampled line transects along the water ways and another fifteen also randomly distributed on the wetlands on a monthly basis. There were three main lifeforms of aquatic macrophytes found in both Sironga and Kapaktet wetlands namely, emerged, submerged and floating, which were dominated by Centella asciatica and Cyperus sp. and the floating macrophytes, Potamogeton schwenfurthii dominated Kapaktet wetland. The study found that macrophyte distribution, abundance and biodiversity were highly affected by predominant economic activities resulting to wetland conversion, nutrient influxes and unsustainable exploitation of macrophytes. We recommend a further study focusing on effects of sedimentation resulting from unsustainable agricultural practices on water quality and macrophytes diversity, distribution and abundance, the effects of changing land-use practices and how different environmental agencies can be involved in the advocacy, conservation and management of the riverine wetlands.

Macrophyte Diversity and Ecosystem Services in Wetlands of Eastern Ranchi: A Multi-site Analysis of Abundance, Frequency, and Importance Value Index Patterns

Macrophytes, visible aquatic and semi-aquatic plants, are integral components of wetland ecosystems, playing crucial roles in maintaining biodiversity, providing ecosystem services, and ensuring ecological stability. This research examines the distribution, abundance, frequency, diversity, and ecosystem services of macrophytes in several wetlands (W1-W7) located in the eastern part of Ranchi district, Jharkhand, India. The study sites include Bundu Lake, Hindalco Pond, Choga Bada Talab, Raja Bandh, Kita Uparbandh, Tamar Bada Talab, and Rukka Dam. A quantitative assessment using quadrat sampling and phytosociological methods was conducted from September 2022 to March 2023 to ensure accurate data collection and analysis. The study documented 78 macrophyte species belonging to 33 families and 58 genera. Emergent macrophytes were found to be the dominant life form, constituting 69% of the recorded species. Several species demonstrated high frequency and abundance across multiple study sites, including Pontederia crassipes Mart., Alternanthera philoxeroides (Mart) Griseb., Hydrilla verticillata (L.f.) Royle, Ipomoea aquaticaForssk., and Nymphoides hydrophyllum (Lour.) kuntze. To assess the diversity and ecological characteristics of the macrophyte communities, various diversity indices were calculated. These included the Shannon-Wiener index, Simpson's index, Margalef index, and Pielou's Evenness index. The results of these analyses revealed high levels of macrophyte diversity and evenness within the studied wetlands. Twenty-one macrophytes were identified as key species and nine species as rare species based on their IVI (Importance Value Index) scores. The key species were found to provide essential ecosystem services, including erosion control, water quality improvement, nutrient cycling, carbon sequestration, and habitat provision for other organisms. This research contributes significantly to our understanding of macrophyte diversity patterns and traits-based ecosystem services in wetland ecosystems. The findings of this study have important implications for the development and implementation of effective conservation strategies for these vital wetland ecosystems in the eastern Ranchi (W1- W7).

Whole-lake coarse woody habitat addition facilitates ecosystem regime restructuring in an oligotrophic lake

Preul-Stimetz T, Shaw SL, Sass GG. 2024. Whole-lake coarse woody habitat addition facilitates ecosystem regime restructuring in an oligotrophic lake. Lake Reserv Manag. XXX-XXX. The loss of vital littoral zone and riparian habitat due to lakeshore residential development is a pervasive issue across temperate aquatic ecosystems. Oligotrophic glacial lakes may be particularly vulnerable to reductions in coarse woody habitat (CWH) due to their lack of alternative structural habitat. Although influences of CWH on fish populations have been well documented, questions remain regarding CWH influences on lower trophic levels and water quality. We conducted a whole-lake CWH addition experiment within a BACI framework using 2 lakes, Sanford (treatment) and Escanaba (reference), in the Northern Highland Lake District of Wisconsin. Premanipulation monitoring began in 2015, trees were dropped in 2018, and data collection continued until 2023. We monitored limnological, planktonic, and benthic macroinvertebrate parameters to test whether CWH addition initiated trophic shifts and altered the structure of the aquatic food web. We found that CWH addition minimally affected water quality and changed some characteristics of Sanford Lake at lower trophic levels. Chlorophyll a concentrations in Sanford Lake significantly increased but Secchi depth was unaffected. The abundance of macrophytes increased in both systems; that in Sanford Lake increased more and was linked to the CWH addition. Dissolved oxygen significantly increased at multiple depth strata. Water temperature was unaffected. We observed declines in total zooplankton that were not related to CWH addition, but the decline in relative abundance of large grazers was. Our results provide a mechanistic understanding of the effects of habitat enhancement at an ecosystem scale and can help guide stakeholder and manager expectations following CWH addition.

Native macrophyte community response to water-level manipulation for an invasive species

Disturbance regimes related to water level fluctuation play an important role in the structuring of aquatic macrophyte communities. In managed systems, winter water level drawdowns have shown promise in controlling populations of nuisance macrophytes, however, drawdowns may have unintended negative consequences on erosion, fauna, and non-target plant species. The Chippewa Flowage, located in Sawyer County, WI, has implemented targeted winter water level drawdowns with the goal of reducing nuisance levels of Myriophyllum spicatum. To evaluate the effects of water level drawdowns on Myriophyllum spicatum and the native macrophyte community, we conducted repeated full lake surveys of aquatic macrophytes at 2018 points under drawdown and normal water level management in 2005/06, 2015, and 2017. We supplemented these efforts with downscaled surveys in 2007, 2010, and 2016. Surveys revealed a statistically significant decline in both Myriophyllum spicatum occurrence and abundance, and average macrophyte abundance during active drawdown management. Kernel distributions of change in point-specific c-value between the two time periods showed a significant increase under drawdown conditions, and a decrease under normal management (D = 0.41, P ≤0.0001). Drawdown management appeared to successfully control Myriophyllum spicatum abundance and allowed for improvements in the floristic quality of the macrophyte community but resulted in reduced macrophyte abundance overall.

Diversity, Abundance, and Seasonal Variation of Aquatic Macrophytes in Southeastern Bangladesh

The study was conducted to assess the diversity and abundance of aquatic macrophytes in the southeastern region of Bangladesh, encompassing the Noakhali, Cumilla, and Chandpur districts. The study was carried out over the period of July 2022 to June 2023. This research utilized a mixed-methods approach, incorporating observation of the study area, qualitative interviews, and quantitative surveys. Five types of aquatic macrophytes, 47 species from 18 orders and 25 families were identified. These are free-floating, rooted-floating, emergent, submerged, and marginal. Among the three locations, Noakhali was recorded as the highest with 44 species, followed by Cumilla with 43, and Chandpur with 35. In Noakhali, seasonal variation analysis showed that 39% of species were found in the rainy season, 14% in summer, 14% in winter, and 20% year-round. In Cumilla, 35% of aquatic macrophytes were available in the rainy season, and 14%, 12%, and 5% in winter, spring, and autumn, respectively. In Chandpur, 37% of aquatic macrophytes were prevalent in the rainy season, 26% were found year-round, 9% in winter, 14% in summer, and 6% each in spring and autumn. In Noakhali, 44% of macrophytes were frequent, 33% moderate, and 23% rare. In Cumilla, 49% were frequent, 44% moderate, and 14% rare. Chandpur reported 49% frequent, 31% moderate, and 20% rare species. The order Alismatales emerged as the dominant order comparatively across all locations. This research will provide insights into the biodiversity of aquatic macrophytes in this area, thus supporting effective management strategies.

Some aspects of the reproductive biology of tilapia black-chinned, Sarotherodon melanotheron (Rüppel, 1852) in relation to macrophyte abundance in three marginal lagoons, Southeast of Côte d'Ivoire

Some aspects of the reproductive biology of tilapia black-chinned, Sarotherodon melanotheron (Rüppel, 1852) in relation to macrophyte abundance in three marginal lagoons, Southeast of Côte d'Ivoire

High diversity of macrophytes in the »green river« Krka (Slovenia)

AbstractThe presence, abundance, and distribution of aquatic macrophytes and their growth forms in the river Krka in Slovenia were studied. The studied slow‐flowing lowland River Krka is also called a »green river« since it is overgrown with macrophytes from its source to its outflow to the river Sava. The environmental parameters of the river ecosystem were also assessed using the modified version of the RCE (Riparian, Channel, and Environmental Inventory) method. Within 24 sections reaching from 100 to 250 m, 23 taxa of macrophytes were found. Sections were distributed noncontinuously from the source to the outflow more or less equally along the river course. The invasive alien species Elodea canadensis reached the highest relative abundance, followed by Ranunculus trichophyllus, Potamogeton crispus, Myriophyllum spicatum, Ceratophyllum demersum, and Potamogeton nodosus. Potamogeton crispus was present in most of the studied sections followed by Nasturtium officinale and M. spicatum. The river offers suitable conditions for the high diversity of macrophytes regarding the type of substrate, low flow velocity, heterogeneity of habitats, and relatively high concentrations of nutrients. In comparison to the survey performed in 2003, when the river Krka was surveyed continuously from the source to the outflow, we found that seven of the submerged and natant macrophytes were not detected in 2020. Macrophytes, growing in the river Krka, indicated meso‐ to eutrophic conditions. Five species recorded in the river Krka are listed on the Red list of endangered species in Slovenia, indicating the need to conserve the river ecosystem.

Late Glacial and Holocene vegetation and lake changes in SW Yakutia, Siberia, inferred from sedaDNA, pollen, and XRF data

Only a few palaeo-records extend beyond the Holocene in Yakutia, eastern Siberia, since most of the lakes in the region are of Holocene thermokarst origin. Thus, we have a poor understanding of the long-term interactions between terrestrial and aquatic ecosystems and their response to climate change. The Lake Khamra region in southwestern Yakutia is of particular interest because it is in the transition zones from discontinuous to sporadic permafrost and from summergreen to evergreen boreal forests. Our multiproxy study of Lake Khamra sediments reaching back to the Last Glacial Maximum 21 cal ka BP, includes analyses of organic carbon, nitrogen, XRF-derived elements, sedimentary ancient DNA amplicon sequencing of aquatic and terrestrial plants and diatoms, as well as classical counting of pollen and non-pollen palynomorphs (NPP). The palaeogenetic approach revealed 45 diatom, 191 terrestrial plant, and 65 aquatic macrophyte taxa. Pollen analyses identified 34 pollen taxa and 28 NPP taxa. The inferred terrestrial ecosystem of the Last Glacial comprises tundra vegetation dominated by forbs and grasses, likely inhabited by megaherbivores. By 18.4 cal ka BP a lake had developed with a high abundance of macrophytes and dominant fragilarioid diatoms, while shrubs expanded around the lake. In the Bølling-Allerød at 14.7 cal ka BP both the terrestrial and aquatic systems reflect climate amelioration, alongside lake water-level rise and woodland establishment, which was curbed by the Younger Dryas cooling. In the Early Holocene warmer and wetter climate led to taiga development and lake water-level rise, reflected by diatom composition turnover from only epiphytic to planktonic diatoms. In the Mid-Holocene the lake water level decreased at ca. 8.2 cal ka BP and increased again at ca. 6.5 cal ka BP. At the same time mixed evergreen-summergreen forest expanded. In the Late Holocene, at ca. 4 cal ka BP, vegetation cover similar to modern conditions established. This study reveals the long-term shifts in aquatic and terrestrial ecosystems and a comprehensive understanding of lake development and catchment history of the Lake Khamra region.

Fluvial avulsions influence soil fertility in the Pantanal wetlands (Brazil)

River avulsions drive important changes in the Pantanal wetlands, owing to their role in the hydro-sedimentology of the region. Although relevant to numerous ecosystem services, few studies have analyzed the influence of river avulsions on soil fertility in the Pantanal. Here, we use the largest ongoing avulsion in the Taquari River (Caronal region) to evaluate the effects on soil fertility, considering two factors: avulsion stage (1) and aquatic-terrestrial succession (2). Since both factors are influenced by macrophyte abundance, an incident map was created through tasseled cap indices from Sentinel 2 images to guide sampling efforts in flooded soils. The mapped area was split into two zones of alluvial processes, the first from the apex of the Caronal lobe corresponding to the Taquari River megafan (TRM), and the second as the distal Paraguay River floodplain (PRF). Soil macro- and micronutrient levels were evaluated from 42 surface samples (0–0.2 m) distributed across the two alluvial process zones. The macrophyte map's overall accuracy (OA) was analyzed by a confusion matrix using the Sentinel 2 imagery. Finally, we used Random Forest regressions to determine the influence of response variables on soil attributes, including tassel indices, distance from the Caronal crevasse, macrophyte density, and an existing soil fertility map. The macrophyte map obtained an OA of 93 %. Some parameters such as pH (r = −0.62; R2 = 0.57), effective cation exchange capacity (r = −0.49; R2 = 0.79), Mn (r = −0.71; R2 = 0.6), Zn (r = −0.69; R2 = 0.54), and base saturation (r = −0.7; R2 = 0.93) were influenced by the distance or level of maturation of the avulsion stage in the TRM. Our scattering of soil collections was insufficient to test the terrestrialization hypothesis (2). The study results show that river channel avulsions influence the accumulation of mineral and organic nutrients in tropical floodplain soils, which has implications for fertility and biodiversity.

Seafloor primary production in a changing Arctic Ocean

Phytoplankton and sea ice algae are traditionally considered to be the main primary producers in the Arctic Ocean. In this Perspective, we explore the importance of benthic primary producers (BPPs) encompassing microalgae, macroalgae, and seagrasses, which represent a poorly quantified source of Arctic marine primary production. Despite scarce observations, models predict that BPPs are widespread, colonizing ~3 million km2 of the extensive Arctic coastal and shelf seas. Using a synthesis of published data and a novel model, we estimate that BPPs currently contribute ~77 Tg C y−1 of primary production to the Arctic, equivalent to ~20 to 35% of annual phytoplankton production. Macroalgae contribute ~43 Tg C y−1, seagrasses contribute ~23 Tg C y−1, and microalgae-dominated shelf habitats contribute ~11 to 16 Tg C y−1. Since 2003, the Arctic seafloor area exposed to sunlight has increased by ~47,000 km2 y−1, expanding the realm of BPPs in a warming Arctic. Increased macrophyte abundance and productivity is expected along Arctic coastlines with continued ocean warming and sea ice loss. However, microalgal benthic primary production has increased in only a few shelf regions despite substantial sea ice loss over the past 20 y, as higher solar irradiance in the ice-free ocean is counterbalanced by reduced water transparency. This suggests complex impacts of climate change on Arctic light availability and marine primary production. Despite significant knowledge gaps on Arctic BPPs, their widespread presence and obvious contribution to coastal and shelf ecosystem production call for further investigation and for their inclusion in Arctic ecosystem models and carbon budgets.

Effects of herbivorous fish on shallow lake ecosystems increase at moderate nutrient conditions

Submerged macrophytes are vital in shallow lakes, as they provide critical ecosystem functions and services and can stabilize the clear-water conditions by various mechanisms. Nutrient enrichment reduces the resilience of macrophyte dominance in shallow lakes, thereby making them susceptible to shifts towards phytoplankton dominance following perturbations. Here, we conducted a mesocosm experiment to examine the individual and combined effects of nutrient enrichment and the addition of grass carp (Ctenopharyngodon idella) on the abundance of submerged macrophytes, epiphyton, and phytoplankton. We hypothesized that moderate nutrient enrichment facilitates macrophyte abundance, but also phytoplankton abundance after macrophyte removal by herbivorous fish. Our data showed that herbivory by grass carp could trigger a shift from macrophytes to algal dominance in mesocosms with moderate nutrient concentrations, but not in those with low nutrient concentrations. Moderate nutrient enrichment alone promoted submerged macrophyte growth, whereas the introduction of grass carp induced a collapse of submerged macrophytes regardless of nutrient conditions. Moreover, the introduction of grass carp showed more negative effects on light conditions of the water column in mesocosms with moderate nutrient concentrations compared to those with low nutrient concentrations. A recovery of submerged macrophytes might thus be limited by low light availability in lakes with moderate nutrient conditions suffering grass carp perturbation. Our results suggest that submerged macrophyte-dominated shallow lakes with moderate nutrient conditions are vulnerable to perturbation by herbivorous fish such as grass carp. In turn, managing the abundance of herbivores in these lakes can support the dominance of macrophytes and associated clear water conditions.

Effects of nutrient enrichment on freshwater macrophyte and invertebrate abundance: A meta-analysis.

External nutrient loading can cause large changes in freshwater ecosystems. Many local field and laboratory experiments have investigated ecological responses to nutrient addition. However, these findings are difficult to generalize, as the responses observed may depend on the local context and the resulting nutrient concentrations in the receiving water bodies. In this research, we combined and analysed data from 131 experimental studies containing 3054 treatment-control abundance ratios to assess the responses of freshwater taxa along a gradient of elevated nutrient concentrations. We carried out a systematic literature search in order to identify studies that report the abundance of invertebrate, macrophyte, and fish taxa in relation to the addition of nitrogen, phosphorus, or both. Next, we established mixed-effect meta-regression models to relate the biotic responses to the concentration gradients of both nutrients. We quantified the responses based on various abundance-based metrics. We found no responses to the mere addition of nutrients, apart from an overall increase of total invertebrate abundance. However, when we considered the gradients of N and P enrichment, we found responses to both nutrients for all abundance metrics. Abundance tended to increase at low levels of N enrichment, yet decreased at the high end of the concentration gradient (1-10 mg/L, depending on the P concentration). Responses to increasing P concentrations were mostly positive. For fish, we found too few data to perform a meaningful analysis. The results of our research highlight the need to consider the level of nutrient enrichment rather than the mere addition of nutrients in order to better understand broad-scale responses of freshwater biota to eutrophication, as a key step to identify effective conservation strategies for freshwater ecosystems.

Loss, resilience and recovery of kelp forests in a region of rapid ocean warming.

Changes in kelp abundances on regional scales have been highly variable over the past half-century owing to strong effects of local and regional drivers. Here, we assess patterns and dominant environmental variables causing spatial and interspecific variability in kelp persistence and resilience to change in Nova Scotia over the past 40 years. We conducted a survey of macrophyte abundance at 251 sites spanning the Atlantic coast of Nova Scotia from 2019 to 2022. We use this dataset to describe spatial variability in kelp species abundances, compare species occurrences to surveys conducted in 1982 and assess changes in kelp abundance over the past 22 years. We then relate spatial and temporal patterns in abundance and resilience to environmental metrics. Our results show losses of sea urchins and the cold-tolerant kelp species Alaria esculenta, Saccorhiza dermatodea and Agarum clathratum in Nova Scotia since 1982 in favour of the more warm-tolerant kelps Saccharina latissima and Laminaria digitata. Kelp abundances have increased slightly since 2000, and Saccharina latissima and L. digitata are widely abundant in the region today. The highest kelp cover occurs on wave-exposed shores and at sites where temperatures have remained below thresholds for growth (21 °C) and mortality (23 °C). Moreover, kelp has recovered from turf dominance following losses at some sites during a warm period from 2010 to 2012. Our results indicate that dramatic changes in kelp community composition and a loss of sea urchin herbivory as a dominant driver of change in the system have occurred in Nova Scotia over the past 40 years. However, a broad-scale shift to turf-dominance has not occurred, as predicted, and our results suggest that resilience and persistence are still a feature of kelp forests in the region despite rapid warming over the past several decades.

Synthesizing the relationships between environmental DNA concentration and freshwater macrophyte abundance: a systematic review and meta-analysis

Synthesizing the relationships between environmental DNA concentration and freshwater macrophyte abundance: a systematic review and meta-analysis

Bottom Biocenoses of Taman Bay (Sea of Azov)

In this research, the species composition and structure of macrophytobenthos, macrozoobenthos, and bottom sediments of the Taman Bay, one of the areas of the Sea of Azov where the seagrass Zostera marina L. forms underwater meadows. The material was collected in 2008–2009 before of the Sea of Azov salinization. Three main zones with different types of bottom sediments (sands, sands with shells and silts) were identified, within which four main macrobenthic biocenoses were located (unvegetated coastal biocenosis, mosaic macrophyte communities outside the surf zone, Z. marina underwater meadows and the central regions’ biocenosis with the dominance of mobile forms of macrozoobenthos and a low abundance of macrophytes). The main environmental factor associated with this distribution of macrophytobenthos was the content of silt (with a granule size of less than 0.001 mm). The spatial structure of the macrozoobenthos correlated with the projective cover of Z. marina. Possible reasons for the revealed regularities in the distribution of communities are discussed.

Heavy Metal Accumulation in Aquatic Macrophytes and Plankton, Water-Sediment in Lake Iznik

This study aims to investigate heavy metal accumulation in water-sediment, plankton, and macrophyte samples of Lake Iznik, one of the important lakes of Turkey. In 2016, water-sediment and plankton samples were taken from 19 and 10 stations respectively. In addition, heavy metal analyzes were performed on samples taken from Potamogeton pectinatus, Najas marina, Myriophyllum spicatum, Typha latifolia, Schoenoplectus litoralis, Phragmites australis, which are the most abundant macrophytes in the lake. The data of water and sediment samples were spatially analyzed in GIS and mapped with ArcGIS. In the water samples of Lake Iznik, arsenic (As), mercury (Hg) and in sediment samples, arsenic (As), chromium (Cr), copper (Cu) and nickel (Ni) were detected at remarkable levels. The results revealed that Iznik Lake was under pressure in terms of heavy metals and their effects should be reduced.

Effects of an Introduced Benthivorous Fish on Macroinvertabrates Diversity in a Semiarid Shallow Lake

The Cyrinus carpio Linnaeus, 1758 (common carp) is a widely introduced species for commercial purposes. However, its detrimental effects on lakes and reservoirs, such as a decrease in water quality, abundance and richness of macrophytes, and macroinvertebrate abundance, are also known. In this study, we investigated the effect of common carp introduction on the macroinvertebrate community in a shallow lake in the Brazilian semiarid region. The study in Panati lake took place between 2002 and 2008 with the introduction of common carp in 2004. Shallow lakes from Our results showed that after common carp introduction, there was a significant reduction in the richness and diversity of the macroinvertebrate community, as well as an increase in the dominance of certain groups, such as chironomids. The decrease in richness and diversity is likely a result of the decline in abundance of key dominant benthic groups and species, such as the gastropods Pomacea lineata (Spix, 1827), Biomphalaria straminea (Dunker, 1848), Aplexa marmorata (Guilding, 1828) and Plesiophysa ornata (Haas 1938), oligochaetes, and ostracods, as well as several insect families. This decline may also lead to increased variability (destabilizing effect) among gastropods, annelids, and crustaceans, as well as an increase in the variability of richness and diversity among benthic macroinvertebrate species

Response of diatom communities to climate and human disturbance: A 4200-year record from Costa Rica

This study integrates diatom analysis with existing records of pollen, charcoal, elemental composition, and stable light isotopes to expand upon the 4200-year history of human activity and climate change from Laguna Los Mangos in southern Pacific Costa Rica. We counted diatoms in peroxide-treated samples and analyzed community composition using cluster analysis, revealing four distinct assemblage zones with diatom variability most closely correlated with phosphorus, titanium, and organic content. The earliest assemblage (Zone D, 4150–3430 cal yr BP) was dominated by Encyonema silesiacum and Nitzschia incognita and aligned with a period of deforestation, erosion, and abundant macrophytes. Gomphonema affine proliferated in Zone C (3430–2450 cal yr BP), reflecting increased pH and productivity likely caused by agriculture-induced nutrient loading. We attributed the preservation gap from 3290 to 2970 cal yr BP in Zone C to silica depletion and erosional deposition that induced decline in diatom abundance by diluting valve concentrations in lake sediments. Nitzschia incognita and G. affine became the dominant taxa in Zone B (2450–1400 cal yr BP), likely reflecting eutrophy, increasing conductivity, and drying climate. Dominance of Diadesmis confervacea indicated reduced lake level in Zone A (1400 cal yr BP–modern) at the onset of the Terminal Classic Drought (TCD). A hiatus in the record indicates lake desiccation from 950 to 450 cal yr BP. During the Little Ice Age (LIA), diatoms reflect conditions similar to Zone B indicating increased lake level, circumneutral pH, and eutrophy. Refilling of the lake indicates increased precipitation during the LIA despite evidence of severe regional drought reported at other sites. Variable precipitation during this period likely resulted from the combined effects of Spanish contact, agricultural collapse, forest recovery, and shifts in Atlantic and Pacific climate forcing mechanisms. Overall, the Los Mangos diatom record reflects shallow, slightly alkaline, eutrophic conditions influenced by nutrient enrichment, erosion, and deforestation associated with maize agriculture.

The recovery of a shallow lake within an agricultural landscape of Minnesota—an interdisciplinary approach to understanding change

Perleberg DJ, Anderson JP, Streitz AR. 2023. The recovery of a shallow lake within an agricultural landscape of Minnesota—an interdisciplinary approach to change. Lake Reserv Manage. 39:311–326.This case study of Lake Shaokatan, Minnesota, reveals how long-term climate, hydrology, water chemistry, and macrophyte data can explain and predict shallow lake phase shifts. After decades of agricultural landscape nutrient loadings, lake and watershed management efforts successfully reduced summer mean total phosphorus and chlorophyll a concentrations to levels that met standards set specifically for shallow lakes in the Northern Glaciated Plains ecoregion (0.09 mg/L and 0.03 mg/L, respectively). The lake “flipped” from a turbid, phytoplankton-dominated phase (<20% macrophyte occurrence) to a clear, macrophyte-dominated phase (annual average of 90% occurrence), and the Minnesota Pollution Control Agency removed it from the state’s impaired waters list. A paired groundwater and lake water quality investigation was critical in understanding how increased precipitation might affect lake water quality, the relationship between groundwater and surface water in this system, and how compounds such as chloride and phosphorus are transported through the watershed. Lakewide macrophyte occurrence has been sustained for at least 7 yr. While abundant macrophyte growth helps maintain a clear water state, it can also create recreational boating issues. Lake managers question how long the lake will remain in the present clear phase as lake users weigh the recreational and aesthetic differences between the 2 phases.