1) Quantify the potential export of detached kelp biomass from commercial production facilities.
2) Map transport pathways and ‘deposit areas’ for exported kelp.
3) Investigate impact and fate of exported kelp on sea floor habitats under and in vicinity to production sites.
Growing kelp produce considerable amounts of detritus, as blade erosion, partial fragmentation, or entire dislodgement. Detached kelp will be transported downstream with the current flow, and eventually settle at the seafloor. Export from natural kelp forests is estimated to ~80% of the standing biomass per year (20% is internal turnover). Expected export of cultivated kelp is less, however preliminary data suggest substantial export. The potential environmental impact will depend on the type of ‘deposit area’, the total biomass per unit time, and nutrients (N) and phosphorous (P).
In 'worst case' scenarios like during heavy storms, physical detachment will increase considerably, and include large kelp fractions, or even whole farms might collapse and export massive amounts of kelp to the surroundings. The environmental impact will be regulated by the balance between the biomass accumulation and the degradation ‘efficiency’ at the seafloor habitat, i.e. the tipping point for when kelp detritus is a food source or a threat to the natural environment.
In the chosen study region (western and central Norway) sea urchins are absent and microbial degradation is the dominating process for kelp detritus breakdown. Numerical model simulations (SINMOD), in situ impact studies and mesocosms experiments will be carried out to target the objectives. Empirical data are expected to be collected during ‘normal operation’, while ‘worst-case’ scenarios will be assessed using modelling and extrapolation of empirical in situ and mesocosms data.
T2.1 Estimate export of kelp detritus. ‘Normal operation’ kelp detritus export will be estimated in situ using a novel labelling technique enabling estimates of specific growth, loss of biomass, and fraction size (leaf length). Time series from early spring through the production period will be completed at SES. Exported TOC and nutrients (N and P) will be calculated combining data from T3.1. Preliminary data from test facilities will support the estimates (Fieler unpub.) The kelp module of SINMOD will be updated based on the empirical data and used to extrapolate detritus export to future and ‘worst-case’ scenarios (all kelp biomass lost, WP1).
T2.2. Transport pathways and ‘deposit areas’ for exported kelp will be simulated using a high resolution (~30 m) 3D hydrodynamic model with particle tracking modules coupled with the kelp growth model (WP1). The "numerical particles" will be equipped with biomass, composition (C:N ratios and water content) and density, so that transport ways, total deposited biomass, deposit areas and size ranges can be computed. Data will make available detailed spatial distribution maps of accumulated kelp, and be guiding the in situ sampling and measurements (T2.3, 2.4).
T2.3 Impact studies on seafloor biodiversity and function. In situ documentation of kelp deposit areas will be assessed using underwater video and SPI camera surveys. Benthic macrofauna (>1 mm) abundance and diversity will be estimated from grab samples across a density gradient of kelp detritus (including TOC, total N, grain size). Different indexes for species compositions will be calculated to assess the ‘ecological quality’ of deposit areas, compared to control sites. Species will be assigned functional traits related to morphology, physiology, phenology and behaviour in order to describe and quantify ecosystem functioning. Data will support assessment of changes in ecosystem functioning and form guidelines for monitoring methods (WP5).
T2.4 Impact of kelp detritus; tipping point between food source or ecosystem threat. State-of-the-art "Eddy Covariance" (EC) measurements will be applied in situ to estimate the sea floor net O2 consumption and demand at deposit areas and at controlled sites. EC measurements resolve sea floor O2 consumption and current velocity non-invasively and in situ continuously (4Hz) over periods for days to weeks. EC landers will be deployed using SCUBA across detritus gradients at deposit areas downstream from SES. EC investigations will provide solid in situ data on effects on sea floor habitats quantify the tipping point of kelp detritus being a food source or threat to sea floor habitats. Findings will be compared KELPPRO – Potential impacts on coastal ecosystems Page 8 of 14 with KELPEX (RCN, 2016-2018) which address the biogeochemical fate of export of biomass from natural kelp forests.
T2.5 Fate and bio-availability of exported kelp will be investigated and quantified from laboratory experiments (Solbergstrand research facility, NIVA) through mesocosms set-ups carefully designed to address the degradation time of kelp (Saccharina and Alaria) under controlled conditions (as a function of biomass, detritus particle size, O2 availability, and flow velocity). The experiments will provide data on degradation time, oxygen demand for degradation, CO2 production, and nutrient release rates (oxic/anoxic N and P turnover).
• Paper on kelp detritus export (C, N, P), fate, and impact on sea floor biodiversity and ecosystem functioning.
• Paper on kelp detritus being a food source or ecosystem threat: an in situ Eddy Covariance study.
• Paper on degradation and bioavailability of kelp detritus as function of detritus size and O2 availability: a mesocosms study
• Input to WP5