Marine transitional zones (MTZs), such as coastal lagoons, tidal inlets, estuaries, and bays form an interface between marine and terrestrial environments. MTZs are often highly dynamic and variable systems, where complex physical and biogeochemical processes from marine and freshwater environments interact. Mixing of Nutrients and contaminants-rich freshwater discharge with sea water results a continuum in salinity and a gradient of chemical, physical, and biological components in the water column. Therefore, MTZs are important zones for nutrient and elemental cycling, primary productivity, fisheries recruitment and human wellbeing. However MTZs are also now vulnerable to multiple stressors like global warming, sea level rise, eutrophication, deoxygenation, increasing concentrations of atmospheric CO2 etc. that can act in different ways on ecosystems requiring careful assessment of the action of each stressor on the key biogeochemical processes occurring in MTZs. EPA and Marine Institute Ireland funded project Nuts&Bolts addresses knowledge gaps with regard to the impact of multiple environmental stressors on the biogeochemical cycling of nutrients, elements (trace metals), and carbon in Ireland's marine transitional waters. We focus on 4 main themes in this project; 1) fluvial derived elemental fluxes through MTZs to the sea 2) nutrient controls on primary productivity in MTZs 3) bio-optics of MTZs and 4) production and consumption of climate relevant gases in MTZs. We collect surface and deep water samples from selected MTZs mainly in west coast of Ireland; Kinvarra Bay, Corrib River, Lough Furnace, Shannon Estuary, Wexford, and Sligo Harbour for the analysis of nutrients (Nitrate, Nitrite, Phosphate, Silicate, ammonia, and urea), FDOM/CDOM, trace metals and REEs, picoplankton abundance (flow cytometry), and climate relevant dissolved gases (O2, N2, Ar, CO2, DMS by Membrane Inlet Mass Spectrometry) in transitional waters. Recent results in more detail will be presented.