Key findings to date
A selection of the key findings of the Turf2Surf project are listed below.
- Annual net primary productivity (ANPP) in the Conwy sits below the mean UK levels on average. Rates within habitats are comparable
- Annual net primary productivity:
- Is predictable from simple soil metrics (NO3, pH and Total-P) on one unified gradient irrespective of soil, habitat or climate
- Foliar nutrient ratios are not good indicators of nutrient limitation as plants are well adapted to their environments
- Photosynthesis rates are not good indicators of overall ANPP due to other traits and ecological processes which down-regulate i.e. production is sink not source controlled.
- A new soil-P method is better able to identify plant-available-P than total-P
- Carbon turnover in soil
- C turnover in soils is C limited as soil available C:N:P is always below microbial C:N:P of 70:7:1
- In arable systems available C:N ratios < 5 leads to phosphorus limitation of C turnover
- C turnover in deep soils is highly responsive to change in C,N and P availability
- Wetlands are completely consistent with other soils in their behaviour across the C:N:P gradient. Anoxia does not change the relationship.
Riparian and river network
- Clear differences in C/N/P ratios between landscapes, largely along an established ecological gradient and reflect land cover and geology
- Complex picture of nutrient losses spatially and temporally through events: dilution, mobilisation, seasonal and flow influences can all be detected
- Definition of riparian zone depends on issue to be considered
- Aquatic DOM production, related to N and P
- Aquatic DOM decomposition/respiration, related to C lability
- DOM concentration same down system, but transformation occurs
- P begins to limit algal growth only at 11 ug P/l, CNP additions stimulate algal growth
- N and P – sources and hydrological processes dominate dynamics
- Fine scale dynamics important for abiotic-biotic interactions (e.g. Si and P limits during bloom development)
- For flux estimation to sea, reach-scale losses important, but not subtle abiotic-biotic coupling not needed
River Estuarine Transition Zone
- Estuarine turbidity maximum (ETM) created by landward advection of SPM resuspended from intertidal flats.
- In upper estuary, flood tide velocities > ebb tide velocities (common in meso/macrotidal estuaries) but due to density stratification on the flood tide, flood turbulence < ebb turbulence (new). Suppression of turbulence limits resuspension of SPM by the flood tide – decreases landward transport of SPM especially of larger flocs (new).
- Aggregation and sedimentation of flocs in ETM at HW in the tidally influenced river.
- Large flocs resuspended on ebb tide, ETM re-created and advected seawards.
- Results in floc size fractionation – large flocs move seawards into main estuary, small flocs move landwards into tidally influenced river (new).
- Particulate nutrient and pathogen concentration peaks map on to SPM concentration peaks (new).
- RETZ and estuarine solutes driven by river, whilst RETZ and estuarine particulates driven by sea.
Integrated assessment and modelling
- aNPP is key explanatory variable of plant biodiversity
- River flow is very important in terms of nutrient distribution in estuaries;
- Wetter winters will flush nutrients to the sea, drier summers will increase trapping;
- Sources dominate instream N and P dynamics, ratios and concentrations except in clean, upland systems (where N, P prime DOM production);
- Lowlands - instream processing is a secondary effect on N and P dynamics, though reach scale losses important for accurate flux determination, and N and P prime DOM production