Nutrient budgets for the Bohai Sea: Implication for ratio imbalance of nitrogen to phosphorus input under intense human activities.

Eutrophication is a global problem for coastal ecosystems, one that the Bohai Sea (BHS), China, is severely afflicted by due to rapid economic and social development over the last forty years. For sustainable nutrients management in the BHS, comprehensive budgets for Nitrogen (N) and Phosphorus (P) was characterized in 2017, and the relative contributions of river input, submarine fresh groundwater discharge, atmospheric deposition, sediment diffusion, and exchange with the Yellow Sea were quantified. The annual N and P fluxes into the BHS were 362 × 103 t and 10.4 × 103 t, respectively. The terrigenous N inputs occupied the highest proportion, while the largest P input was from sediment diffusion. The ratio of N:P was 77 for total external inputs, while that of the Yellow River was 680; both exceeded the Redfield ratio, indicating an imbalance in the nutrient structure and a P limitation in the BHS.

Periodic density as an endpoint of customized plankton community responses to petroleum hydrocarbons: A level of toxic effect should be matched with a suitable time scale.

As an endpoint of community response to contaminants, average periodic density of populations (APDP) has been introduced to model species interactions in a community with 4 planktonic species. An ecological model for the community was developed by means of interspecific relationship including competition and predation to calculate the APDP. As a case study, we reported here the ecotoxicological effects of petroleum hydrocarbons (PHC) collected from Bohai oil field on densities of two algae, Platymonas subcordiformis and Isochrysis galbana, a rotifer, Brachionus plicatilis, and of a cladocera, Penilia avirostris, in single species and a microcosm experiment. Time scales expressing toxic effect increased with increasing levels of toxic effect from molecule to community. Remarkable periodic changes in densities were found during the tests in microcosm experiment, revealing a strong species reaction. The minimum time scale characterizing toxic effect at a community level should be the common cycle of population densities of the microcosm. In addition, the cycles of plankton densities shortened in general with increasing PHC, showing an evident toxic effect on the microcosm. Using APDP as the endpoint, a threshold concentration for the modeled microcosm was calculated to be 0.404 mg-PHC L-1. The APDP was found to be more sensitive and reliable than the standing crops of populations as the endpoint. This indicated that the APDP, an endpoint at the community level, could be quantitatively related to the endpoints at the population level, and led to the quantitative concentration-toxic effect relationship at the community level.

Compound eutrophication index: An integrated approach for assessing ecological risk and identifying the critical element controlling harmful algal blooms in coastal seas.

Current ecological risk assessment and controlling element identification methods of harmful algal blooms (HABs) are not connected. Here, we identified the controlling elements by correlation and principal component analyses, and the analytic hierarchy process. A compound eutrophication index (CEI) integrating risk assessment with controlling element identification was constructed and verified using data collected from Jiaozhou Bay, China. The CEI results agreed with the chlorophyll-a concentration and the main eutrophication assessment results. The HAB risk assessment of the CEI was more efficient than that of the nutrient quality index and Assessment of Estuarine Trophic Status. The contribution ratio of the loads and concentrations of nutrients (nitrogen, phosphorus, and chemical oxygen demand) to HABs in Jiaozhou Bay was 70%. In the high-risk areas, the contribution ratio of nutrients to HABs was 77%. Therefore, terrestrial nutrient inputs must be reduced to prevent and control HABs in the north-eastern areas of Jiaozhou Bay.

Long-term changes in nutrient regimes and their ecological effects in the Bohai Sea, China.

The nutrient regime has changed significantly in the Bohai Sea (BS) during the past six decades because of anthropogenic perturbations. Specifically, the concentration of DIN increased by about 7-fold from the end of the 1950s to the mid-2010s, while DIP and DSi concentrations decreased from the end of the 1950s to the beginning of the 1990s, and have since increased again. Unsynchronized changes in nutrient levels have led to changes in the nutrients structure, which has caused a series of ecological effects. Phytoplankton biomass increased by 6-fold from the 1960s to the mid-2010s. Additionally, phytoplankton composition shifted from a diatom-dominated to a dinoflagellate-dominated system, and the dominant species of macrozoobenthos changed. Red tides rarely occurred before the 1980s, but have occurred periodically and frequently since the 1990s. Finally, the BS ecosystem has shifted from an N-limited oligotrophic state before the 1990s to a potentially P-limited eutrophic state.

[Potential Bioavailability of Dissolved Organic Nitrogen in the Discharge Outlets of Sewage Treatment Plants Around the Jiaozhou Bay].

Dissolved organic nitrogen (DON) is an important portion of total dissolved nitrogen (TDN) transported to the coastal from land-based sources and its bioavailable moieties of DON are regarded as potentially important nitrogen sources for eutrophication in coastal environments. Based on the four field observations conducted in July, November 2012 and in March, May 2013 at the four sewage treatment plants (STPs) around the Jiaozhou Bay (JZB), the concentrations and compositions of total dissolved nitrogen (TDN) as well as total dissolved amino acids (TDAA) were analyzed, and the ratio of dissolved organic carbon (DOC) to DON and the composition and abundance of amino acids were regarded as indexes to evaluate the bioavailability of DON in STPs around JZB. The concentrations of TDN ranged from 413.10 µmol L⁻¹ to 3,580.65 µmol · L⁻¹ and showed a seasonal variation tendency, which were higher in March and November and lower in May and July, and the percentages of DON to TDN varied from 2.14% to 88.75%. In the discharge outlets of STPs around JZB, the values of DOC/DON were low and ranged from 0.2 mol · mol⁻¹ to 26.2 mol · mol⁻¹ with an average of (5.05 ± 6.39) mol · mol⁻¹, while the values of TDAA/DOC were high and ranged from 0.33% to 3.02% with an average of 1.54% ± 0.78%. Based on TDAA/DOC, the bioavailable proportion of the dissolved organic matter was estimated, which accounted for 0.44% to 46.97%. In conclusion, DON in the discharge outlets of STPs around JZB possessed high bioavailability and might contribute to the eutrophication of coastal water in JZB.

Rhamnolipids enhance marine oil spill bioremediation in laboratory system.

This paper presents a simulated marine oil spill bioremediation experiment using a bacterial consortium amended with rhamnolipids. The role of rhamnolipids in enhancing hydrocarbon biodegradation was evaluated via GC-FID and GC-MS analysis. Rhamnolipids enhanced total oil biodegradation efficiency by 5.63%, with variation in normal alkanes, polyaromatic hydrocarbons (PAHs) and biomakers biodegradation. The hydrocarbons biodegradation by bacteria consortium overall follows a decreasing order of PAHs>n-alkanes>biomarkers, while in different order of PAHs>biomarkers>n-alkanes when rhamnolipids was used, and the improvement in the removal efficiency by rhamnolipids follows another order of biomarkers>n-alkanes>PAHs. Rhamnolipids played a negative role in degradation of those hydrocarbons with relatively volatile property, such as n-alkanes with short chains, PAHs and sesquiterpenes with simple structure. As to the long chain normal alkanes and PAHs and biomakers with complex structure, the biosurfactant played a positive role in these hydrocarbons biodegradation.

[Evaluation on biodegradability of hydrocarbon biomarkers in two crude oils under laboratory conditions].

Biodegradabilities of several hydrocarbon biomarker groups, including isoprene, hopanes and steranes in a medium-crude oil BZ34-1 and a heavy-crude oil SZ36-1 from offshore, were determined under laboratory conditions. The results of GC-MS analysis showed that isoprene biomarkers such as pristane and phytane in both crude oils degraded obviously in 60-day experiment period. The degradation ratios of pristane and phytane in the medium-crude oil BZ34-1 reached 20.2% and 15.0%, respectively; while those in the heavy-crude oil SZ36-1 reached 95.6% and 75.4%, respectively. Pristane and phytane in the heavy-crude oil SZ36-1 were degraded in the early period of biodegradation, but these two biomarkers in the medium-crude oil BZ34-1 were degraded in middle and late biodegradation phases. However, hopanes and steranes in the both oils were not biodegraded obviously during the whole period. These results indicated that pristane and phytane could be used to evaluate bioremediation efficiency in the early biodegradation phase for light or medium oils, while hopanes and steranes could be used to evaluate bioremediation efficiency within the whole given experiment process.