Gennadi Lessin

Modelling impacts and recovery in benthic communities exposed to localised high CO2

Regulations pertaining to carbon dioxide capture with offshore storage (CCS) require an understanding of the potential localised environmental impacts and demonstrably suitable monitoring practices. This study uses a marine ecosystem model to examine a comprehensive range of hypothetical CO2 leakage scenarios, quantifying both impact and recovery time within the benthic system. Whilst significant mortalities and long recovery times were projected for the larger and longer term scenarios, shorter-term or low level exposures lead to reduced projected impacts. This suggests that efficient monitoring and leak mitigation strategies, coupled with appropriate selection of storage sites can effectively limit concerns regarding localised environmental impacts from CCS. The feedbacks and interactions between physiological and ecological responses simulated reveal that benthic responses to CO2 leakage could be complex. This type of modelling investigation can aid the understanding of impact potential, the role of benthic community recovery and inform the design of baseline and monitoring surveys.

Modelling the influence of Major Baltic Inflows on near-bottom conditions at the entrance of the Gulf of Finland

A coupled hydrodynamic-biogeochemical model was implemented in order to estimate the effects of Major Baltic Inflows on the near-bottom hydrophysical and biogeochemical conditions in the northern Baltic Proper and the western Gulf of Finland during the period 1991–2009. We compared results of a realistic reference run to the results of an experimental run where Major Baltic Inflows were suppressed. Further to the expected overall decrease in bottom salinity, this modelling experiment confirms that in the absence of strong saltwater inflows the deep areas of the Baltic Proper would become more anoxic, while in the shallower areas (western Gulf of Finland) near-bottom average conditions improve. Our experiment revealed that typical estuarine circulation results in the sporadic emergence of short-lasting events of near-bottom anoxia in the western Gulf of Finland due to transport of water masses from the Baltic Proper. Extrapolating our results beyond the modelled period, we speculate that the further deepening of the halocline in the Baltic Proper is likely to prevent inflows of anoxic water to the Gulf of Finland and in the longer term would lead to improvement in near-bottom conditions in the Baltic Proper. Our results reaffirm the importance of accurate representation of salinity dynamics in coupled Baltic Sea models serving as a basis for credible hindcast and future projection simulations of biogeochemical conditions.

Analysis of temporal variability of measured and modeled vertical distributions of salinity and temperature in the Gulf of Finland during 10-year period

The Gulf of Finland is the sub-basin of the Baltic Sea seriously affected by eutrophication. General Estuarine Transport Model (GETM) was used for modeling hydrophysical fields of the Gulf during the period from 1997 to 2005. The results of the hydrodynamic modeling are important input for ecosystem modeling, in which salinity and temperature variations play the most important role. An accurately simulated salinity field is to some extent a proof that the transport of passive bio-chemical tracers can also be simulated correctly. In this study validation of the results of GETM is performed and comparison with Modular Ocean Model (MOM) is provided. These two models differ in numerical schemes that are used for solving the model equations, in model setup and to some extent in forcing. At first the time series of surface and bottom temperature and salinity from GETM are visually compared with measurements. Long-term measurement data from three HELCOM monitoring stations representing western, central and eastern parts of the Gulf were used. In this study we focus on Taylor diagram that provides quick summary of the degree of patterns correspondence and allows seeing how well model simulates natural pattern. For statistical analysis the surface temperature and salinity have been given the values at a depth of 5 m, and the bottom salinity and temperature are the corresponding values at the lowest depth (about 60 m) at which measurements were carried out. The validation results were grouped similarly for both models. Modeled surface temperature showed good agreement with observed data in all three stations. Root mean square error (RMSE) was between 0.2 and 0.4, correlation coefficients between 0.94 and 0.98 and normalized standard deviations between 0.9 and 1.1 for the both models. Thus, seasonal cycles in the upper layer were reproduced well. Bottom temperatures and surface and bottom salinities were reproduced with lower quality. Bottom temperatures were better reproduced in the western and central Gulf than in the eastern Gulf. Surface salinity was simulated with the same quality in all stations by GETM, while MOM reproduced salinity better in the central Gulf compared to the eastern and western part. Bottom salinities were better simulated by MOM than by GETM. The latter showed larger variability due to higher spatial resolution.

Modelling marine sediment biogeochemistry: Current knowledge gaps, challenges, and some methodological advice for advancement

The benthic environment is a crucial component of marine systems in the provision of ecosystem services, sustaining biodiversity and in climate regulation, and therefore important to human society. With the contemporary increase in computational power, model resolution and technological improvements in quality and quantity of benthic data, it is necessary to ensure that benthic systems are appropriately represented in coupled benthic-pelagic biogeochemical and ecological modelling studies. In this paper we focus on five topical challenges related to various aspects of modelling benthic environments: organic matter reactivity, dynamics of benthic-pelagic boundary layer, microphytobenthos, biological transport and small-scale heterogeneity, and impacts of episodic events. We discuss current gaps in their understanding and indicate plausible ways ahead. Further, we propose a three-pronged approach for the advancement of benthic and benthic-pelagic modelling, essential for improved understanding, management and prediction of the marine environment. This includes: (A) development of a traceable and hierarchical framework for benthic-pelagic models, which will facilitate integration among models, reduce risk of bias, and clarify model limitations; (B) extended cross-disciplinary approach to promote effective collaboration between modelling and empirical scientists of various backgrounds and better involvement of stakeholders and end-users; (C) a common vocabulary for terminology used in benthic modelling, to promote model development and integration, and also to enhance mutual understanding.

Modeling of eutrophication processes in the Gulf of Finland during 1991–2010

The hydrodynamic model GETM coupled with the ecosystem model ERGOM was applied to the Baltic Sea area for the period 1991-2010. The first part of the modeled period is characterized by considerable socioeconomic changes in the area that are generally considered favorable for the status of coastal marine ecosystems due to a decrease in external nutrient loads. Model results were used to describe and analyze changes in salinity, nutrient (nitrate and phosphate) and oxygen dynamics in the central part of the Gulf of Finland, the most eutrophied sub-basin of the Baltic Sea, over the last two decades. Model validation showed very good agreement between modeled and measured parameters in the Gulf. In the surface layer nitrates were slightly underestimated, while phosphates were overestimated during the second half of the modeled period. Near-bottom parameters were generally accurately reproduced. Model results show that in fact the eutrophication status of the Gulf of Finland has worsened during the last two decades, especially during the latter part of the modeled period. This is reflected in an increased frequency of anoxic events and consecutive high phosphate loading and decrease of near-bottom nitrate concentrations. Stronger stratification favors anoxic conditions in the near-bottom, while a decrease in salinity induced by mixing processes allows for oxygenation of deep areas. However, the effect of these mixing events is short-term and deep water quickly returns to the anoxic state.

Modeling the response of the Gulf of Finland ecosystem to changing climate

Direct and indirect effects of changing meteorological conditions include alterations in nutrient cycling, timing and extent of algal blooms, species composition and oxygen dynamics of the Baltic coastal ecosystems. In this study the one-dimensional water column model GOTM coupled with a modified version of the biogeochemical model ERGOM was implemented to study the effects of changes in meteorological forcing associated with climate change on dynamics of nutrients, phytoplankton and dissolved oxygen in the central part of the Gulf of Finland. The modeling period from 1997 to 2008 (11 years) was chosen. Initial distributions of salinity, temperature and biogeochemical parameters from available measurement data were prescribed. As a reference run representing the present conditions of the ecosystem, model results with real atmospheric forcing were used. The model results were validated using observational data from the HELCOM monitoring program. The first three years of the simulation were used as a spin-up period. For the rest of the period modeled ecosystem sensitivity to variations in wind speed, air temperature, cloud cover and precipitation were analyzed separately and in a combination. The ranges of variations were chosen in agreement with recent publications on the assessment of climate change in the Baltic Sea region. Results have shown that increase in precipitation does not have any remarkable effect on the ecosystem. Increase in wind speed intensifies water mixing thus providing more nutrients for phytoplankton, but also slightly decreases water temperature. Change in cloud cover negatively affects phytoplankton growth due to decrease in light availability during biologically active period. Increased air temperature influences phytoplankton growth rates, leading to enhanced sedimentation of organic matter and near-bottom oxygen consumption. The scenario which combined all the previous, showed similar results as change in air temperature only, but slightly closer to the reference run due to action of wind speed and cloud cover. The study has shown that regardless of known limitations of one-dimensional models, they are a valuable tool in the investigation of marine ecosystem properties and their sensitivity to changes in the forcing parameters.

Defining the extent of coastal zone for ecosystem-based management

Two different approaches in defining coastal zone extent exist. One of them sets fixed boundaries to the coastal zone, and, thus, is easily adopted by decision-makers. Another approach follows distribution of a set of contiguous ecosystems, and is more accordant with the ecosystem-based management of the coastal zone. Ecological approach requires comprehensive research of the system in focus. However, managers usually need more general tools which allow a first-order assessment of ecosystem structure and functioning. This work demonstrates how results of ecohydrodynamic model can be used by managers in the assessment of coastal ecosystem status and proposes mapping of characteristic coastal zone regions for management purposes.