Ecological impact of other (non-soluble reactive) phosphorus fractions

A case study from:

Phosphorus is an essential element for all life and is widely recognised as a key factor influencing the status of river and lake ecosystems. Much past research and monitoring work in these ecosystems has 
focussed on an individual fraction of the total phosphorus pool, operationally termed soluble reactive phosphorus. However, an extremely wide range of non-soluble reactive forms of phosphorus may exist 
in freshwaters. Therefore, the objectives of this project were to:

• provide an independent assessment of the state of research knowledge regarding non-soluble reactive forms of phosphorus in rivers and lakes,
• identify key priorities for future research and monitoring work in this area, and
• consider the potential for development of a typology system to describe the ecological impacts of non-soluble reactive forms of phosphorus in rivers and lakes across the United Kingdom. 

Approach

To address these objectives, a literature review was undertaken to assess current state of research and semi-structured interviews were conducted by staff from Lancaster University with 12 experts drawn 
from a range of research specialisms and organisations. 

Conclusions

• Phosphorus must be understood as an inherently non-conservative element, rapidly cycled between multiple physical, chemical and biological compartments in river and lake ecosystems.
• Almost all forms of phosphorus within freshwater ecosystems should be seen as potentially bioavailable, due to multiple transformation mechanisms that have the potential to increase phosphorus bioavailability.
• A long-standing evidence base demonstrates that non-soluble reactive phosphorus could have ecological impacts within freshwaters, including the potential for organisms to use these forms 
  of phosphorus to meet their metabolic demand for phosphorus or carbon.
• Significant uncertainty surrounds the actual ecological impacts of non-soluble reactive forms of phosphorus in natural ecosystems. In particular, the role of soluble reactive phosphorus 
  concentration, of variation in bioavailability across the diverse range of non-soluble reactive phosphorus forms, and of factors such as nitrogen and carbon availability are priorities for future research.
• Significant conceptual, knowledge and data challenges face the development of any typology system designed to represent variation in the ecological risks posed by non-soluble reactive forms of phosphorus in rivers and lakes.

Implications for wastewater treatment

The water industry is currently investing heavily in phosphorus removal from wastewater to protect the water environment. This investment is regulated using limits of total phosphorus concentrations in final effluent. There were concerns that regulation by total phosphorus would deliver over-treatment, and that soluble reactive phosphorus would deliver the required environmental protection at reduced cost to customers. The conclusions of rapid cycling of non-soluble reactive phosphorus between fractions, and potential bioavailability of almost all forms of phosphorus, improved confidence in regulation by total phosphorus limits. This confidence does, however, remain open to challenge due to uncertainty around the actual ecological impacts of non-soluble reactive forms of phosphorus in natural ecosystems.

Matt Hill, on the project steering group for Yorkshire Water, said, ‘Investment of customers’ money in environmental protection must be driven by the best information available. The project gave the water industry the most up to date information possible on the suitability of total phosphorus limits to regulate that investment. Although open to further challenge, the project confirmed that total phosphorus limits are currently the best way to manage environmental risk from phosphorus in wastewater final effluent.