Biogeochemical Budgets of Nutrients and Metabolism in the Curonian Lagoon (South East Baltic Sea): Spatial and Temporal Variations

Estuaries are biogeochemical reactors able to modulate the transfer of energy and matter from the watershed to the coastal zones and to retain or remove large amounts of terrestrially generated nutrients. However, they may switch from nutrient sink to source depending upon interannual variability of the nutrient supply and internal processes driving whole system metabolism (e.g., net autotrophic or heterotrophic). We tested this hypothesis in the Curonian Lagoon, a hypertrophic estuary located in the south east Baltic Sea, following the budget approach developed in the Land-Ocean Interactions in the Coastal Zone (LOICZ) project. Annual budgets for nitrogen (N), phosphorus (P), and silica (Si) were calculated for the 2013–2015 period. The lagoon was divided in a flushed, nutrient loaded area, and in a confined, less loaded area. The lagoon was always a sink for dissolved inorganic Si and P whereas it was a N sink in the confined area, dominated by denitrification, and a N source in the flushed area, due to dinitrogen (N2) fixation. The net ecosystem metabolism (NEM) indicated that the Curonian Lagoon was mainly autotrophic because of high primary production rates. In this turbid system, low N:P ratio, high summer temperatures, and calm weather conditions support high production of N2-fixing cyanobacteria, suppressing the estuarine N-sink role.

Effects of nitrogen and phosphorus on Microcystis aeruginosa growth and microcystin production

In the present study, the effects of nitrogen (N) and phosphorus (P) on the growth of Microcystis aeruginosa and the production of microcystins (MCs) were investigated. The results showed that the growth of M. aeruginosa was not merely determined by N or P, but both nutrients were limiting for the species. Moreover, an excess of N and constant P in the culture medium could stimulate the growth of M. aeruginosa, whereas the growth of the species was inhibited in the culture medium containing excess of P and constant N. The optimal growth of M. aeruginosa was at an N:P ratio of 0.1 with the maximal optical density of 1.197 at 680 nm (OD680), whereas the maximal microcystin-LR (MC-LR) content of 228.2 μg·L−1 observed in the culture medium with an N:P ratio of 5. Interestingly, MC-LR production occurred under conditions of N starvation, thereby suggesting that the growth rate of M. aeruginosa was not related to MC-LR production under conditions of nutrient stress.

Kelimpahan Dinoflagellata Bentik Berbahaya di Habitat Lamun dan Makroalga di Pulau Pari, Kepulauan Seribu, Indonesia

<p class="Papertext"><strong>The Abundance of the Harmful Benthic Dinoflagellate in the Seagrass and Macroalgae Habitats on Pari Island, Thousand Islands, Indonesia. </strong>Benthic dinoflagellates are an important part of benthic ecosystems and part of their ecological functions. However, ciguatoxin (CTX) producer dinoflagellates, which could cause Ciguatera Fish Poisoning (CFP) disease, is a known threat to marine biota and the island’s coastal communities, such as in Pari Island. Thus, this research aimed is to study the population of five harmful and toxin producer benthic dinoflagellate genera, namely <span style="text-decoration: underline;">Amphidinium</span>, <span style="text-decoration: underline;">Coolia</span>, <span style="text-decoration: underline;">Gambierdiscus</span>, <span style="text-decoration: underline;">Ostreopsis</span>, and <span style="text-decoration: underline;">Prorocentrum</span>, in macroalgae and seagrass habitats of Pari Island. Benthic dinoflagellate samples were collected in Juni 2019 using artificial substrates in the form of a 10×15 cm nylon screen. Environmental variables, such as nutrient concentration (nitrogen and phosphorus) and water temperature were also measured. The results showed that the average benthic dinoflagellate density in seagrass habitats was four times higher compared to the macroalgae habitats. <em>Gambierdiscus</em> were found as the most abundant benthic dinoflagellate in seagrass habitats, while <em>Prorocentrum</em> were more abundant in macroalgae habitats. Principal Component Analysis (PCA) showed that the N:P ratio was the most important regulating parameter for most benthic dinoflagellate genera in this study, except <em>Ostreopsis</em>, which was found to be more abundant in phosphorus-rich macroalga habitats. The data also shows an increase of benthic dinoflagellate cell density up to seven times compared to the previous research data in 2012 and 2013. That trend indicates an increase in the disturbance and pressure on the macroalgae and seagrass habitats of Pari Island, which require special attention to prevent the occurrence of toxic Benthic Harmful Algal Blooms (bHABs) and CFP cases in the island.</p>

The Water Quality and Nutrients Status in the Dungun River Basin, Terengganu

This study investigated the spatial variation of nitrogen (N)-based and phosphorus (P)-based nutrients together with water quality parameters (temperature, pH, dissolved oxygen, biological oxygen demand, chemical oxygen demand and total suspended solids) in the Dungun River basin, Terengganu. The Water Quality Index (WQI) of the river was applied according to the Malaysian Department of Environment (DOE-WQI) and classified based on the Malaysian National Water Quality Standard (NWQS). Results showed that the major source of nutrients and water quality deterioration in the basin was most likely due to the effluent discharged from the nearby palm oil factory. The overall WQI mean value obtained was 85.44%, which indicated that the Dungun River basin was in a clean condition and categorised into Class II based on the NWQS classification. The overall mean mass N:P ratio was 19.8:1 which indicated that the algal growth was generally controlled by the P-based nutrients. Based on this study, it is suggested continuous monitoring necessary to be carried out for proper management of this river basin.

Acid Phosphatase Activity in Freshwater Ecosystems of Western Cuba and its Relationship with Water Quality

Enzyme activity plays an important role in the functioning of aquatic ecosystems. It is sensitive to changes in environmental conditions such as pH, temperature, and nutrient concentration. The objective of this work was to determine the acid phosphatase activity (AcPA) in the Almendares and San Juan rivers (western Cuba) and its relationship with physicochemical and microbiological indicators. For this purpose, AcPA, temperature, pH, total dissolved solids, electrical conductivity, dissolved oxygen, concentration of nitrates, nitrites, ammonium, phosphates, total heterotrophs, enterococci, Escherichia coli, thermotolerant coliforms, chlorophyll a and chemical oxygen demand (COD) were determined at three sampling stations on the Almendares River and at three sampling stations on the San Juan River. In addition, the nutrient pollution index (NPI) and the N:P ratio were calculated. In both ecosystems, spatio-temporal variability was observed in the enzymatic activity. In the Almendares River (polluted ecosystem), AcPA was positively correlated with nitrate concentration and COD. While in the San Juan River (slightly contaminated ecosystem) the AcPA correlated negatively with the pH and NPI and positively with the concentrations of total heterotrophs, Escherichia coli, chlorophyll a and the N:P ratio. These results show the impact of anthropogenic pollution on AcPA in freshwater ecosystems with a tropical climate.

The Pattern of Leaf N:P Ratio Along Plantation Age: A Global Synthesis

Background Plant stoichiometry displayed flexible over age sequences in previous studies, but effect of stand age on stoichiometry showed large uncertainties for different plantations at the global scale. In this study, we want to obtain the general pattern of leaf N:P ratio for global plantations across age gradients through the compilation and analysis of published data from the individual studies. Results Stand age, together with life forms, and climatic variables strongly affected leaf N:P ratio. This result indicates that the stand age is an indispensable underlying mechanism on stoichiometry. Leaf N:P ratio increased with stand age for all plantations pooled together, revealing the existence of the general pattern in leaf stoichiometry for plantations across age gradients. Leaf N:P ratio exhibited no trend in evergreen trees, but an increasing trend was obtained in deciduous trees along age sequences. Meanwhile, leaf N:P ratio rose with stand age for plantations in humid subtropical regions, but it did not vary in dry temperate regions. Conclusions Our results reveal the effects of age on tree stoichiometry cannot be neglected. These age-related patterns of stoichiometry verified that global plantations changed from N limitation to P limitation with increasing stand age, particularly for deciduous plantations and in plantations in humid regions. The study highlights the importance of considering stand age when exploring nutrient patterns in plantations, which contributes to improving the plant stoichiometry theory and offers a guidance for the nutrient management of plantations at regional to global scales.

Nutrient Alteration Drives the Impacts of Seawater Acidification on the Bloom-Forming Dinoflagellate Karenia mikimotoi

Seawater acidification and nutrient alteration are two dominant environmental factors in coastal environments that influence the dynamics and succession of marine microalgae. However, the impacts of their combination have seldom been recorded. A simulated experimental system was set up to mimic the effects of elevated acidification on a bloom-forming dinoflagellate, Karenia mikimotoi, exposed to different nutrient conditions, and the possible mechanism was discussed. The results showed that acidification at different pH levels of 7.6 or 7.4 significantly influenced microalgal growth (p&lt;0.05) compared with the control at pH 8.0. Mitochondria, the key sites of aerobic respiration and energy production, were impaired in a pH-dependent manner, and a simultaneous alteration of reactive oxygen species (ROS) production occurred. Cytochrome c oxidase (COX) and citrate synthase (CS), two mitochondrial metabolism-related enzymes, were actively induced with acidification exposure, suggesting the involvement of the mitochondrial pathway in coping with acidification. Moreover, different nutrient statuses indicated by various N:P ratios of 7:1 (N limitation) and 52:1 (P limitation) dramatically altered the impacts of acidification compared with those exposed to an N:P ratio of 17:1 (control), microalgal growth at pH 7.4 was obviously accelerated with the elevation of the nutrient ratio compared to that at pH 8.1 (p&lt;0.05), and nutrient limitations seemed beneficial for growth in acidifying conditions. The production of alkaline phosphatase (AP) and acid phosphatase (AcP), an effective index indicating the microalgal growth status, significantly increased at the same time (p&lt;0.05), which further supported this speculation. However, nitrate reductase (NR) was slightly inhibited. Hemolytic toxin production showed an obvious increase as the N:P ratio increased when exposed to acidification. Taken together, mitochondrial metabolism was suspected to be involved in the process of coping with acidification, and nutrient alterations, especially P limitation, could effectively alleviate the negative impacts induced by acidification. The obtained results might be a possible explanation for the competitive fitness of K. mikimotoi during bloom development.

Impact of River Damming on Downstream Hydrology and Hydrochemistry: The Case of Lower Nestos River Catchment (NE. Greece)

In this paper, a series of field surveys were carried out along the Nestos River watershed (NE Greece) to assess the influence of two hydropower dams (Thissavros and Platanovrisi) upon the hydrology, hydrochemistry and nutrients stoichiometry of the river. Results showed that Nestos hydrology, downstream of the reservoirs, is entirely governed by the man-induced hydropower-driven dam retention/release policy. Dams’ operation increased the retention of dissolved inorganic nitrogen (DIN) and total suspended solids (TSS) significantly, affecting their downstream fluxes, even under water release regime. On the contrary, dams’ construction and operation did not seem to influence the downstream fluxes of dissolved inorganic phosphorus (DIP) and silica (DSi), although these elements also depended on the releasing policy. DIN retention, combined with the dependence of DIP to the water level of Thissavros, resulted in alteration of the N:P ratio at the downstream part. Almost all nutrients were stored at the bottom layer of Thissavros reservoir, especially under the summer stratification regime. Platanovrisi reservoir acts as a buffer zone between Thissavros and the Nestos downstream part. Anoxic conditions in the reservoirs favour the transformation of nitrates into ammonia and the remineralization of phosphorus from sediments, creating a degraded environment for freshwater fauna.

Phosphorus Losses to Surface Runoff Waters After Application of Digestate to a Soil Over Fertilised with Phosphorus

Anaerobic digestates from biogas plants can be used as agricultural fertilisers providing recycling nitrogen (N) and other nutrients for crop needs. It is still unclear the impact on phosphorus (P) losses to runoff waters of digestates as sources of N instead of inorganic N fertilisers in over fertilised soils with P. A field experiment was done in a sandy and acidic soil high in P. The experimental design was completely randomised with five treatments. The inorganic N fertilisation (90 kg ha−1) was done in four treatments, those with past P inputs of the following: (i) inorganic N and P fertilisers (Ni/MF), (ii) organic amendments (pig or duck dry slurry-Ni/PS and Ni/DS or cattle manure compost-Ni/CM). Digestate was applied in plots with past P input of cattle slurry (DG/CS) providing also 90 kg N ha−1. Ryegrass was sowed as cover crop. The concentration of total dissolved P in runoff waters was high in all treatments and ranged between 0.5 (Ni/PS) and 2.6 mg L−1 (DG/CS). These runoff waters pose a risk of non-source P pollution for fresh waters. In soils with low P sorption capacity and over fertilised with P, the fertilisation with anaerobic digestate as the only source of N to crops increased the risk of P losses to runoff waters compared with inorganic N fertilisation. Therefore, the amount of digestate applied to soil must be calculated considering its N:P ratio in order to not exceed the crop P requirement.