Other inputs to estuarine and coastal systems Flashcards
What inputs, other than riverine, are there into estuarine and coastal systems?
Atmospheric Submarine groundwater discharge Trace gases Glacial inputs Benthic sources
What is dry deposition of aerosols & wet deposition in atmospheric inputs?
Dry deposition of aerosols = direct fallout of particles to sea surface and subsequent dissolution.
Wet deposition = rain; washes out particles so some material dissolves.
Where are atmospheric N inputs to coastal seas mainly derived from?
- combustion sources releasing NO/NO2 to the atmosphere, where it ultimately forms HNO3 or NO3-
- agricultural emissions which release principally NH3
How are atmospheric N inputs distributed?
They’re dispersed throughout the coastal zone (not a point source, like rivers)
How much can atmos N inputs contribute to total land-based inputs of N to larger coastal seas?
20-30%
Why is there a measurable increase in the surface ocean water lead concentrations?
Due to combustion of leaded petrol
What is the main source of mercury in the ocean?
atmospheric deposition
What is the nature of the origin of trace gases?
directly or indirectly biological
What are the features of methane as a trace gas?
- produced by anaerobic microbial processes
- contributes ~15% of radiative global forcing
- mostly comes from sediments, but can be produced at pycnocline
- oxygenated surface waters on coastal shelves supersaturated with CH4- ; the ‘methane paradox’
What are the features of N2O as a trace gas?
- contributes around 6% of global radiative forcing
- by-product of microbial nitrification & intermediate during microbial denitrification
- mean surface saturation in shelf seas ~109%, but in estuaries ~600%
What are the features of dimethylsulfide as a trace gas?
- produced by phaeocytis, coccolithophores and dinoflagellates
- oxidised in the troposphere, contributing to atmospheric acidity & formation of cloud condensation nuclei
- fluxes are higher in summertime
- on average estuarine and coastal waters contribute ~8% of total global DMS emissions
What is submarine groundwater discharge?
direct flow of groundwater into the ocean.
SGD = meteoric water + connate water + recirculated water
What are the driving forces and contributing factors of meteoric waters in submarine groundwater discharge?
driving forces - hydraulic gradient
contributing factors - topography, transmissivity, precipitation, evapotranspiration
What are the driving forces and contributing factors of recirculated waters in submarine groundwater discharge?
driving forces - hydraulic gradient, tidal pumping, wave setup
contributing factors - tidal range, freq, period, wind force & direction
What are the driving forces and contributing factors of connate waters in submarine groundwater discharge?
driving forces - density, thermal gradient
contributing factors - geology, geothermal heating
What are some components of submarine groundwater discharge?
- significant impact on biogeochemical cycling
- both freshwater & salt water components, so wide range in salinity
- usually occurs as slow diffuse flow but can be found as large point sources
What are some methods for quantifying SGD?
- infrared imaging (high lats - SGD warm rel to ocean; low lats - SGD cooler)
- direct measurements (seepage meters)
- tracer techniques (natural and artificial)
Why are benthic (sedimentary) sources important?
- ultimate long term repository (sink) for elements & particles introduced to marine waters
- active recycling of many elements at benthic interface & longer timescale release of materials into the water column
Water flux from SDG?
Water flux from SDG is ~6-10% of the river water flux, but fluxes of chem components can be much higher (even exceeding river fluxes)
