Total Algal Biomass Research Articles

High resolution chlorophyll- a in-situ fluorescence sensors versus in-vitro chlorophyll- a measurements in mesocosms with contrasting nutrient and temperature treatments.

Harmful algal blooms (HABs) are a significant threat to freshwater ecosystems, and monitoring for changes in biomass is therefore important. Fluorescence in-situ sensors enable rapid and high frequency real-time data collection and have been widely used to determine chlorophyll- a (Chla) concentrations that are used as an indicator of the total algal biomass. However, conversion of fluorescence to equivalent Chla concentrations is often complicated due to biofouling, phytoplankton composition and the type of equipment used. Here, we validated measurements from 24 Chla and 12 phycocyanin (cyanobacteria indicator) fluorescence in-situ sensors (Cyclops-7F, Turner Designs) against spectrophotometrically (in-vitro) determined Chla and tested a data-cleaning procedure for eliminating data errors and impacts of non-photochemical quenching. The test was done across a range of freshwater plankton communities in 24 mesocosms (i.e. experimental tanks) with a 2x3 (high and low nutrient x ambient, IPCC-A2 and IPCC-A2+50% temperature scenarios) factorial design. For most mesocosms (tanks), we found accurate (r 2 ≥ 0.7) calibration of in-situ Chla fluorescence data using simple linear regression. An exception was tanks with high in-situ phycocyanin fluorescence, for which multiple regressions were employed, which increased the explained variance by >16%. Another exception was the low Chla concentration tanks (r 2 < 0.3). Our results also show that the high frequency in-situ fluorescence data recorded the timing of sudden Chla variations, while less frequent in-vitro sampling sometimes missed these or, when recorded, the duration of changes was inaccurately determined. Fluorescence in-situ sensors are particularly useful to detect and quantify sudden phytoplankton biomass variations through high frequency measurements, especially when using appropriate data-cleaning methods and accounting for factors that can impact the fluorescence readings.

Density-dependent facilitation and inhibition between submerged and free-floating plants

This study aimed at testing the hypothesis that free-floating plants may facilitate the growth of submerged plants under hypertrophic conditions and intermediate plant density. The effects of Lemna presence on the growth of two submerged plants (Elodea nuttallii and Ceratophyllum demersum) over a nitrogen gradient were experimentally investigated. This was complemented with analysing the presence of C. demersum and E. nuttallii in Hungary and in Germany in relation to the density of free-floating plants. Results showed a negative exponential pattern between underwater light intensity and Lemna cover. Ceratophyllum and Elodea relative growth rate decreased with increasing nitrogen concentrations and additional low Lemna density stimulated Ceratophyllum and suppressed Elodea. Elodea decreased linearly with Lemna density while Ceratophyllum showed a unimodal response. Total algal biomass (epiphytic and planktonic) was higher in Ceratophyllum than in Elodea treatments and decreased rapidly with increasing Lemna density. The field studies showed a positive relationship between Ceratophyllum and a negative one between Elodea and free-floating plant cover. This study clearly showed that free-floating plants can have either facilitating or inhibiting impact on the growth of submerged plants depending on cover density and macrophyte species. The facilitating effect on Ceratophyllum is most likely due to suppressing epiphytic algal growth.

Warming reshapes the invertebrate predation pressure on the plankton community

Abstract Climate change stressors, including warming and heatwaves, can alter plankton composition and dominance patterns in temperate shallow lakes, which can disrupt ecosystem function and curtail ecosystem services. Understanding how these alterations could take place under future climates is therefore important. To understand such changes, we performed a year‐long mesocosm experiment with controls reflecting present temperature conditions and a treatment reflecting a future climate change scenario, including heatwaves of 5–8°C above ambient water temperatures. In the warmer conditions, the predatory invertebrate Mesostoma, exerted a strong top‐down control on Daphnia, resulting in a switch in herbivore dominance to Ceriodaphnia in contrast to the controls where Daphnia remained dominant. A complementary predation experiment revealed that Mesostoma fed at a higher rate on Daphnia than on Ceriodaphnia and cyclopoid copepods. Cyclopoids were the least affected taxon but showed tendencies to sustain populations longer into the winter at elevated temperatures. Moreover, both total algal and cyanobacteria biomass increased with warming. Our experiments suggest that predator–prey dynamics may alter plankton community composition and dominance patterns in a warmer climate because thermophilic predatory invertebrates have the potential to induce cascading food‐chain effects and alter the herbivore dominance patterns in lake zooplankton. This may have implications for the algal population dynamics and overall ecosystem function and processes in shallow lakes.

Experimental Study on the Impact of Pulsed Flow Velocity on the Scouring of Benthic Algae from a Mountainous River

The decrease in periodic scouring of pulsed flows in regulated rivers can result in algal communities dominated by filamentous algae, not available as food sources for fish and macroinvertebrates. To study the pulsed flow velocity required to scour benthic algae from natural river beds, the removal effects on the algal biomass and resistances of different species were tested in a laboratory flume at different velocities of 0.8, 1.1, 1.4, 1.7, and 2.0 m/s. The removal of total algal biomass showed a significant positive relationship with increasing velocities, which reached 22% at 2.0 m/s. The biomass removal of green algae and diatoms was higher than that of blue–green algae. The flow velocity at 1.4 m/s had a clear removal effect on filamentous algae. The velocity higher than 1.7 m/s caused a significant increase in the removal percentage of total biomass dominated by diatoms and blue–green algae. To reduce the filamentous algae and retain the diatoms and blue–green algae, a range of near bed flow velocity was suggested to be 1.4–1.7 m/s. This range could serve as a reference for required pulsed flow velocity to reduce the growth of excessive or nuisance periphyton.

Evaluation of Food Web Structure and Complexity in the Process of Kelp Bed Recovery Using Stable Isotope Analysis

Kelp forests have declined gradually all over the world. Understanding the trophic structure of such a productive and diverse ecosystem is crucial for its restoration and effective management. Few studies, however, have focused on the trophic structure and functional recovery of kelp forests in the process of restoration. This study was conducted in the eastern coast of Korea where kelp bed restoration was in process with the removal of sea urchins. In addition to quantitative measurement for recovery using common community parameters, we investigated how fast the stability of a food web structure could be established in the newly restored kelp beds with an initially barren condition, using stable isotope analysis, in comparison with a nearby natural bed and barren site. At the restored bed, total algal biomass and diversity reached the levels of the natural bed within 1 year. While the δ13C and δ15N values of macroalgae and organic matter were separated isotopically, they were similar among sites, excluding organic matter at the natural bed in 2019. Most consumers showed similar isotopic values among sites, with overlapping range for δ13C of producers. However, some herbivores showed higher δ15N values as predators/omnivores, particularly at barrens, which could be explained by trophic plasticity depending on the macroalgal structure. In the restored bed, for the first year, higher trophic diversity (CR, CD) and lower trophic redundancy (MNND, SDNND) showed non-overlapping &amp;gt;50% CIs among sites. However, this distinctive stage moved toward the natural bed upon entering the second year as trophic diversity decreased and trophic redundancy increased while natural bed overlapped at&amp;lt;50% CIs. The recovery speed in this system was fast (1 year for quantitative perspectives and 2 years for functional completion). After removing the sea urchins, recruitment of macroalgae quickly increased concomitantly with consumer groups, boosting the diversity and trophic structure of the restored bed. The trophic structure of the first year of restoration was not an intermediate stage toward the completion, but a transient over-shooting state. This might have been triggered by the fast introduction of diverse macroalgae to the urchin-free bare rock space, providing an interesting finding needed to be tested in other temperate marine systems.

Remote sensing of column-integrated chlorophyll a in a large deep-water reservoir

The accurate assessment of total algal biomass in large deep-water reservoirs is challenging because the characteristics of thermodynamic stratification in such reservoirs differ noticeably from those of other types of inland waters. To address this challenge, we proposed a novel remote sensing model to derive column-integrated chlorophyll a (CIC), a better indicator than water surface chlorophyll a concentration (Csurf), for evaluating total algal biomass. The proposed algorithm was utilized to construct the patterns of spatiotemporal change in CIC in the Xin’anjiang Reservoir (the largest freshwater human-made reservoir in East China, located in Zhejiang Province) based on 97 cloud-free Sentinel-2 satellite images from 2016 to 2020. The results showed that the best index for developing the CIC remote sensing model was the average chlorophyll a concentration within the euphotic layer, which could be derived from Csurf and euphotic depth. The proposed model demonstrated good performance in deriving CIC in the Xin’anjiang Reservoir from Sentinel-2 images (yielding a mean absolute percent error of 20.7% and a root mean square error of 16.3 mg/m2). The values of the five-year averaged CIC and total algal biomass within the reservoir were 62.38 mg/m2 and 22.31 t, respectively. The CIC in the Xin’anjiang Reservoir displayed noticeable spatial variation, with the highest CIC appearing in the riverine zone and the lowest CIC appearing in the lacustrine zone. Clear seasonal variation in CIC was observed, with CIC exhibiting the order summer > autumn > spring > winter. Although the model was developed for a specific reservoir, we believe that this research can serve as a case study that illustrates the benefits of using CIC for assessing spatiotemporal variation in phytoplankton.

Predators mitigate the destabilising effects of heatwaves on multitrophic stream communities.

Amidst the global extinction crisis, climate change will expose ecosystems to more frequent and intense extreme climatic events, such as heatwaves. Yet, whether predator species loss-a prevailing characteristic of the extinction crisis-will exacerbate the ecological consequences of extreme climatic events remains largely unknown. Here, we show that the loss of predator species can interact with heatwaves to moderate the compositional stability of ecosystems. We exposed multitrophic stream communities, with and without a dominant predator species, to realistic current and future heatwaves and found that heatwaves destabilised algal communities by homogenising them in space. However, this happened only when the predator was absent. Additional heatwave impacts on multiple aspects of stream communities, including changes to the structure of algal and macroinvertebrate communities, as well as total algal biomass and its temporal variability, were not apparent during heatwaves and emerged only after the heatwaves had passed. Taken together, our results suggest that the ecological consequences of heatwaves can amplify over time as their impacts propagate through biological interaction networks, but the presence of predators can help to buffer such impacts. These findings underscore the importance of conserving trophic structure, and highlight the potential for species extinctions to amplify the effects of climate change and extreme events.

Influence of Potamogeton crispus on Lake Water Environment and Phytoplankton Community Structure

The decomposition of submerged macrophytes is generally associated with dramatic changes in the water environment, such as the large release of nutrients (e.g., nitrogen and phosphorus) and organic carbon to the surrounding waters, which may result in significant changes in phytoplankton community structure. In this study, Potamogeton crispus, physicochemical variables, and phytoplankton samples were collected in 14 shallow lakes in the middle and lower Jianghuai Plain in spring (growing period of P. crispus) and summer (decomposition phase of P. crispus) of 2018. The effects of the decline of P. crispus on water quality and phytoplankton community structure were quantified. The results showed that water transparency increased significantly in spring because the growth of P. crispus inhibits sediment resuspension and macrophytes can transport the nutrients from the water column to the sediment. The values of dissolved oxygen and pH also increased significantly due the photosynthesis by macrophytes. In contrast, the decomposition of P. crispus during summer months caused a significant increase in water turbidity and organic matter. There were considerable differences in phytoplankton biomass and cyanobacterial biomass in the sites with or without P. crispus, and the corresponding ratios of cyanobacterial biomass to the total algal biomass were 18.96% and 34.05%, respectively. Higher values of cyanobacterial biomass were observed with the decomposition of P. crispus than its counterpart in summer because ① the decomposition of macrophytes provided sufficient organic matter and nutrient (nitrogen and phosphorus) resources for cyanobacterial growth; ② P. crispus decline in summer significantly increased water turbidity, which makes cyanobacteria occupy a better ecological niche and more efficiently utilize nitrogen and phosphorus.

Nutrients and warming interact to force mountain lakes into unprecedented ecological states.

While deposition of reactive nitrogen (N) in the twentieth century has been strongly linked to changes in diatom assemblages in high-elevation lakes, pronounced and contemporaneous changes in other algal groups suggest additional drivers. We explored the origin and magnitude of changes in two mountain lakes from the end of the Little Ice Age at ca 1850, to ca 2010, using lake sediments. We found dramatic changes in algal community abundance and composition. While diatoms remain the most abundant photosynthetic organisms, concentrations of diatom pigments decreased while pigments representing chlorophytes increased 200-300% since ca 1950 and total algal biomass more than doubled. Some algal changes began ca 1900 but shifts in most sedimentary proxies accelerated ca 1950 commensurate with many human-caused changes to the Earth System. In addition to N deposition, aeolian dust deposition may have contributed phosphorus. Strong increases in summer air and surface water temperatures since 1983 have direct and indirect consequences for high-elevation ecosystems. Such warming could have directly enhanced nutrient use and primary production. Indirect consequences of warming include enhanced leaching of nutrients from geologic and cryosphere sources, particularly as glaciers ablate. While we infer causal mechanisms, changes in primary producer communities appear to be without historical precedent and are commensurate with the post-1950 acceleration of global change.

Hurricane Irma’s Impact on Water Quality and Phytoplankton Communities in Biscayne Bay (Florida, USA)

The short-term (< 6 months) effects of Hurricane Irma on water quality and phytoplankton community structure were assessed in Biscayne Bay and the adjacent coastal canals from September 2017 through January 2018. The bay experienced sharp fluctuations in daily average salinity and salinity gradients during the passage of the hurricane and significant decreases in salinity as a result of increased freshwater inflows that followed the hurricane (148.2% increase in total inflows in the first week after the hurricane compared to a week before). These decreases were most pronounced in southern and south-central parts of the bay, which experienced the largest post-hurricane increases in freshwater inflows (349.4% and 103.1% in southern and south-central parts of the bay, respectively). Storm-induced increases in inorganic nutrient concentrations stimulated phytoplankton growth in northern, north-central, and southern parts of the bay. Opportunistic phytoplankton taxonomic groups such as chlorophytes and cyanobacteria dominated the total algal biomass pool in the canals, and northern and southern parts of the bay in the weeks following the storm, but they were gradually outcompeted by diatoms in the following months. Changes in spatial-temporal phytoplankton community structure in the months following Hurricane Irma reflect recovery and return to usual seasonal patterns. The effect of Hurricane Irma on water quality and phytoplankton communities was short-lived (< 3 months), suggesting that Biscayne Bay is resilient to tropical cyclones.

Modeling Benthic Versus Hyporheic Nutrient Uptake in Unshaded Streams With Varying Substrates

AbstractAssessments of riverine ecosystem health and water quality require knowledge of how headwater streams transport and transform nutrients. Estimates of nutrient demand at the watershed scale are commonly inferred from reach‐scale solute injections, which are typically reported as uptake velocities (vf). Multiple interacting processes control vf, making it challenging to predict how vf responds to physical changes in the stream. In this study, we link vf to a continuous time random walk model to quantify how vf is controlled by in‐stream (velocity, dispersion, and benthic reaction) and hyporheic processes (exchange rate, residence times, and hyporheic reaction). We fit the model to conservative (NaCl) and nitrate (NO3−‐N) pulse tracer injections in unshaded replicate streams at the Notre Dame Linked Experimental Ecosystem Facility, which differed only in substrate size and distribution. Experiments were conducted over the first 25 days of biofilm colonization to examine how the interaction between substrate type and biofilm growth influenced modeled processes and vf. Model fits of benthic reaction rates were ∼8× greater than hyporheic reaction rates for all experiments and did not vary with substrate type or over time. High benthic reactivity was associated with filamentous green algae coverage on the streambed, which dominated total algal biomass. Finally, vf was most sensitive to benthic reaction rate and stream velocity, and sensitivity varied with stream conditions due to its nonlinear dependence on all modeled processes. Together, these results demonstrate how reach‐scale nutrient demand reflects the relative contributions of biotic and abiotic processes in the benthic layer and the hyporheic zone.

Copper Affects Composition and Functioning of Microbial Communities in Marine Biofilms at Environmentally Relevant Concentrations.

Copper (Cu) pollution in coastal areas is a worldwide threat for aquatic communities. This study aims to demonstrate the usefulness of the DNA metabarcoding analysis in order to describe the ecotoxicological effect of Cu at environmental concentrations on marine periphyton. Additionally, the study investigates if Cu-induced changes in community structure co-occurs with changes in community functioning (i.e., photosynthesis and community tolerance to Cu). Periphyton was exposed for 18 days to five Cu concentrations, between 0.01 and 10 μM, in a semi-static test. Diversity and community structure of prokaryotic and eukaryotic organisms were assessed by 16S and 18S amplicon sequencing, respectively. Community function was studied as impacts on algal biomass and photosynthetic activity. Additionally, we studied Pollution-Induced Community Tolerance (PICT) using photosynthesis as the endpoint. Sequencing results detected an average of 9,504 and 1,242 OTUs for 16S and 18S, respectively, reflecting the high biodiversity of marine periphytic biofilms. Eukaryotes represent the most Cu-sensitive kingdom, where effects were seen already at concentrations as low as 0.01 μM. The structure of the prokaryotic part of the community was impacted at slightly higher concentrations (0.06 μM), which is still in the range of the Cu concentrations observed in the area (0.08 μM). The current environmental quality standard for Cu of 0.07 μM therefore does not seem to be sufficiently protective for periphyton. Cu exposure resulted in a more Cu-tolerant community, which was accompanied by a reduced total algal biomass, increased relative abundance of diatoms and a reduction of photosynthetic activity. Cu exposure changed the network of associations between taxa in the communities. A total of 23 taxa, including taxa within Proteobacteria, Bacteroidetes, Stramenopiles, and Hacrobia, were identified as being particularly sensitive to Cu. DNA metabarcoding is presented as a sensitive tool for community-level ecotoxicological studies that allows to observe impacts simultaneously on a multitude of pro- and eukaryotic taxa, and therefore to identify particularly sensitive, non-cultivable taxa.

Structure and Productivity of the Phytocenosis in the Southwestern Kara Sea in Early Spring

Results of plankton biota studies in the southwestern Kara are presented. The spatial distribution of hydrochemical and hydrophysical parameters related to structural and functional characteristics of phytoplankton in the surface water is considered. The chlorophyll a concentration varied in the surface layer of the Kara Sea from 0.08 to 3.22 mg m–3 (mean value 0.62 mg m–3). Primary production varied from 0 to 1.92 mg C m–3 day–1 (the mean value of 0.42 mg C m–3 day–1) in the ice-covered water areas and was greater by a factor of four, ranging from 1.01 to 3.46 mg C m–3 day–1 (the mean value of 1.79 mg C m–3 day–1) in ice-free areas. In this case, the total algal biomass varied from 0.8 to 110.7 mg C m–3 (mean value 10.6 mg C m–3). It is shown that in the study period, waters from the western Kara Sea were more productive than the estuarine water areas of the Ob and Yenisei rivers. The activity of phototrophic phytoplankton in river waters was almost completely absent. It is established that the contents of nutrients and iron were higher than the threshold for limitation of phytoplankton development. The experiments showed that the production activity of phototrophic algae is restrained by light deficit beneath the ice.

Spatial differences in dissolved silicon utilization in Lake Baikal, Siberia: Examining the impact of high diatom biomass events and eutrophication

AbstractRecent research has highlighted how Lake Baikal, Siberia, has responded to the direct and indirect effects of climate change (e.g., ice‐cover duration), nutrient loading, and pollution, manifesting as changes in phytoplankton/zooplankton populations, community structure, and seasonal succession. Here, we combine and compare analyses of chlorophyll a (an estimate of total algal biomass), carotenoid pigments (biomarkers of algal groups), and lake water silicon isotope geochemistry (δ30SiDSi) to differentiate spatial patterns in dissolved silicon (DSi) uptake at Lake Baikal. A total of 15 sites across the three basins (south, central, and north) of Lake Baikal were sampled in August 2013 along a depth gradient of 0–180 m. Strong, significant correlations were found between vertical profiles of photic zone DSi concentrations and δ30SiDSi compositions (r = −0.81, p &lt; 0.001), although these are strongest in the central basin aphotic zone (r = −0.98, p &lt; 0.001). Data refute the hypothesis of DSi uptake by picocyanobacteria. Algal biomass profiles and high surface δ30SiDSi compositions suggest greater productivity in the south basin and more oligotrophic conditions in the north basin. δ30SiDSi signatures are highest at depth (20 m) in central basin sites, indicating greater (10–40%) DSi utilization at deep chlorophyll maxima. DSi limitation occurs in the pelagic central basin, probably reflecting a high diatom biomass bloom event (Aulacoseira baicalensis). Meanwhile in the more hydrologically restricted, shallow Maloe More region (central basin), both high δ30SiDSi compositions and picocyanobacteria (zeaxanthin) concentrations, respectively point to the legacy of an “Aulacoseira bloom year” and continuous nutrient supply in summer months (e.g., localized eutrophication).

Temporal Variation of Nitrogen and Phosphorus Species Distribution on Total Phytoplankton Biomass in Eutrophic Lakes

To aid in the eutrophication management, the relationships between total algal biomass in response to varying nitrogen and phosphorus species concentrations, Volatile (VSS), and Total Suspended (TSS) solids in the water column were investigated. Sampling was conducted at the deepest portion of the reservoir for analysis of phosphorus, nitrogen, chlorophyll a, VSS, and TSS.

Alterations in microbial community composition with increasing &amp;lt;i&amp;gt;f&amp;lt;/i&amp;gt;CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;: a mesocosm study in the eastern Baltic Sea

Abstract. Ocean acidification resulting from the uptake of anthropogenic carbon dioxide (CO2) by the ocean is considered a major threat to marine ecosystems. Here we examined the effects of ocean acidification on microbial community dynamics in the eastern Baltic Sea during the summer of 2012 when inorganic nitrogen and phosphorus were strongly depleted. Large-volume in situ mesocosms were employed to mimic present, future and far future CO2 scenarios. All six groups of phytoplankton enumerated by flow cytometry ( &lt; 20 µm cell diameter) showed distinct trends in net growth and abundance with CO2 enrichment. The picoeukaryotic phytoplankton groups Pico-I and Pico-II displayed enhanced abundances, whilst Pico-III, Synechococcus and the nanoeukaryotic phytoplankton groups were negatively affected by elevated fugacity of CO2 (fCO2). Specifically, the numerically dominant eukaryote, Pico-I, demonstrated increases in gross growth rate with increasing fCO2 sufficient to double its abundance. The dynamics of the prokaryote community closely followed trends in total algal biomass despite differential effects of fCO2 on algal groups. Similarly, viral abundances corresponded to prokaryotic host population dynamics. Viral lysis and grazing were both important in controlling microbial abundances. Overall our results point to a shift, with increasing fCO2, towards a more regenerative system with production dominated by small picoeukaryotic phytoplankton.

The dynamics of freshwater phytoplankton stability in the Naroch Lakes (Belarus)

The phytoplankton community of the Belarus Lakes Naroch, Myastro and Batorino, which have a Trophic State Index of 42.3, 60.7 and 66.8, respectively, underwent drastic changes to their structure during the period between 1968 and 2012. Thanks to an extensive monitoring program, these changes were well-documented and were qualitatively interpreted as signs of the community destabilization. The main objective of this study was the quantification of the ecological stability of the phytoplankton community in the Naroch Lakes. The approach to the quantification of ecological stability was based on defining the stability index as an inverse of the Euclidean Distance between the current and the reference states of the algal community (EuD-approach). The stability of the phytoplankton community was characterized by two indices: a “combined” index (SI[Comb]), and a “total community” index (SI[TotB]). SI[Comb] was calculated based on the individual taxonomic group biomasses and thus characterizes the stability of a community structure. SI[TotB] was calculated based on the values of the total algal biomass. Analyses of the results of this study extended the plausibility of the EuD-approach for the quantification of lake phytoplankton stability and allowed us to identify the dynamics of the stability of the Naroch Lakes phytoplankton. For the Naroch Lakes, we observed relatively larger SI[TotB] values in comparison with the SI[Comb] values. The results enabled us to examine the relationship between the lake trophic status and the stability of the phytoplankton community.

Coupling dissolved organic carbon, CO2 and productivity in boreal lakes

Summary Lakes worldwide are in rapid change because of direct or indirect climate impacts. In boreal areas, the increased concentrations of dissolved organic matter (DOM) are profoundly affecting light climate and productivity in multiple ways. Photochemical and microbial mineralisation of DOM are major sources of CO2 in these lakes. It has been suggested that this CO2 could potentially promote primary production and offset negative impacts of increased light attenuation. A synoptic survey of 76 Scandinavian lakes along gradients of DOM and total phosphorus (TP) revealed a major negative impact of DOM on primary production and algal biomass primarily related to light attenuation, whilst a strong positive impact of TP. The negative impact of DOM on lake productivity is thus partly offset by DOM‐associated P. Concentrations of CO2 did not relate significantly to either production, biomass, or seston stoichiometry, and thus whilst elevated CO2 may promote primary production in more productive lakes, it does not in these CO2‐supersaturated boreal lakes. Zooplankton biomass correlated strongly with TP and total algal biomass, less so with primary production, and was negatively related to DOM, likely reflecting the autotroph responses to DOM.

Satellite-Based Estimation of Column-Integrated Algal Biomass in Nonalgae Bloom Conditions: A Case Study of Lake Chaohu, China

In shallow lakes, algal biomass is a fundamental indicator of eutrophication status. However, the vertical movement of phytoplankton within the water column can complicate the determination of total phytoplankton biomass using remotely sensed data of surface conditions. In this study, we develop, validate, and apply a new approach to use remotely sensed reflectance to estimate the variability of total algal biomass in shallow eutrophic lakes. Using the baseline normalized difference bloom index together with hydrological and bathymetric data, we determine the spatial and temporal dynamics of the total algal biomass in Lake Chaohu, a large shallow lake in eastern China under the nonalgae bloom conditions. Over an eleven-year period (2003-2013), the total phytoplankton biomass was highly variable, more than doubling between 2006 and 2007, from 19.95t to 39.50t. The seasonal decomposition of biomass dynamics indicated the highest biomass production occurred in June, while the lowest occurred in April. The estimates of total phytoplankton biomass were both consistent with in situ measurements and consistent for observations made on the same day and on consecutive days. The improved stability and reliability of total biomass estimations provided more complete information about lake conditions with respect to surface concentrations. This has implications for both management and modeling.

Of Rocks and Hard Places: Comparing Biotic Assemblages on Concrete Jetties versus Natural Rock along a Microtidal Mediterranean Shore

ABSTRACT Bonnici, L.; Borg, J.A.; Evans, J.; Lanfranco, S., and Schembri, P.J., 2018. Of rocks and hard places: Comparing biotic assemblages on concrete jetties versus natural rock along a microtidal Mediterranean shore. The species composition and structure of littoral assemblages on concrete jetties were compared with those on natural rocky shores at two localities on the microtidal NE coast of Malta. Algal species richness and total algal biomass were significantly lower on jetties. Faunal species richness and faunal abundance were also lower on jetties, albeit not significantly so. Jetties and natural rocky shores differed in relative species composition. The algae Palisada perforata/Laurencia obtusa and several mobile animals, mostly crustaceans, molluscs, and polychaetes, were more abundant on rocky shores. In particular, the supralittoral gastropod Melarhaphe neritoides had a density ranging between 8 ind./m2 to 98 ind./m2 on rocky shores but was never recorded on jetties. Conversely, the algae Cla...