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Title: Ranunculus in Chalk Rivers Phase 2
Author: E Darby E Cranston
Author: Environment Agency
Document Type: Monograph
Annotation: Environment Agency Project ID:EAPRJOUT_1181, Representation ID: 367, Object ID: 2401
Abstract:
In the last decade following a series of low flow years concern was expressed that Ranunculus in Chalk rivers appeared to be suffering a decline. Factors suggested as affecting Ranunculus include low flows due to changing rainfall patterns, over abstraction, enrichment, siltation and channel management. A large number of surveys and research projects have been conducted on Chalk rivers before and during the 1990s. There was, however, a feeling that the information available was not widely disseminated and needed to be collated and reviewed to more effectively address pressing issues of management and conservation. The aim of this project was to draw together and review all relevant information on Ranunculus in Chalk rivers and recommend a strategy for future management. In Phase 1 of the project source material on Ranunculus in Chalk rivers was gathered together and given a preliminary review against a set of criteria affecting Ranunculus. Relevant material was then collated into a database. Questionna ires on Ranunculus were sent to Environment Agency Areas with Chalk rivers as well as a range of agencies, groups and individuals including riparian owners, river keepers and others with experience of Chalk rivers. Phase 2 of the project involved a more detailed review of the source material. Summaries of the source material and a matrix of aFactorsa and aDriversa affecting Ranunculus, aTypea and aBasis of Informationa together with potential aManagement Applicationsa were compiled and entered onto a database. Additional information on Ranunculus status in Chalk rivers together with details of research and rehabilitation projects were requested from Environment Agency Areas to update the information from Phase 1. The findings of this report therefore are based on the documents reviewed and the information supplied by outside sources. A primary output of the review was to identify the cause and effect of the various influences (Factors and Drivers) on the growth and distribution of Ranunculus. Factors are primarily measurable variables considered to affect Ranunculus growth and Drivers are anthropogenic influences that change the character of the Factors. This knowledge was seen as being potentially useful to the Environment Agency and others in the management of Chalk rivers. The review of the documents has not revealed any numerical measurements for the Factors affecting Ranunculus. The inter-relatedness of the many environmental variables affecting Ranunculus growth creates difficulties in isolating the impacts of the individual Factors. However, the review does show the fundamental importance of the effect of discharge or flow and as a result, velocity. High flows appear, in part at least, to alleviate the impacts of other factors allowing Ranunculus to flourish whereas low flows exacerbate the impacts of other factors. During Phase 2 of the project a total of 311 documents were reviewed of which 172 were accepted as relevant and used in the production of this report. From the information supplied there appears to be a general lack of knowledge of the status of Ranunculus prior to 1990, except on some of the larger rivers. The current status of Ranunculus is also unknown for many stretches of river and even for some whole river lengths. Of 156 listed Chalk rivers, 98 were not mentioned in the documents reviewed. The highest number of citations in the documents is to the Factors of Velocity/Depth/Levels, Discharge/Seasonal Annual Changes, Substrate/Siltation and Light/Shade/Temperature. R and D TECHNICAL REPORT W 1-042/TR v There is quantitative information on the importance of Discharge, Velocity and Light whereas virtually all of the information documented on Substrate/Siltation is qualitative or inferred. The lowest number of citations is to the Factors of Grazing and Physical Dimensions. Generally the documents show that the most reported influences on Ranunculus growth are Factor, rather than Driver, led. Amongst the Drivers the largest number of citations is to Natural Climate Cycles followed by Channel Management and to a lesser extent Enrichment from Point Sources. The large number of documents commenting on Discharge and Ranunculus growth considers this Factor primarily in relation to Natural Climate Cycles. The effect of discharge is universally regarded as of prime importance to the growth and distribution of Ranunculus. There is evidence of the adverse impact on Ranunculus of the drought in 1976 and its subsequent recovery following higher flows e.g. the Rivers Lambourn and Kennet. There was widespread reporting that Ranunculus had suffered in 1989 and early 1990s from the effects of low flows on most Chalk rivers. Ranunculus is now reported to be dominant on many river reaches following two years of higher flows in 1999 and 2000. The reporting of poor growth in low-flow years and then recovery following higher flows is consistent with the conclusions drawn from the documents that Natural Climate Cycles is the key Driver in most cases. Velocity, invariably related to discharge, is acknowledged as being of particular importance to Ranunculus, with low velocity commonly cited as a reason for poor Ranunculus growth. Quantitative data have identified Ranunculus as a plant requiring fast flows to aid the rapid delivery of oxygen and carbon to support its high pho tosynthetic rate. Velocity is also seen to act indirectly by removing potentially competitive or shading algae. Competition is seen to be a major factor affecting Ranunculus growth in Chalk rivers and the main Drivers appear to be Vegetation Management, Light/Shade/Temperature and Enrichment from Point Sources; the effects of which are variously exaggerated or alleviated by discharge. Abstraction is a Driver that can have considerable influence on discharge. Much work has been done on the impacts of abstraction but few of the documents actually describe the impact of abstraction on Ranunculus. The greatest number of references relate to how abstraction affects Ranunculus through its impact on discharge and velocity. There is agreement that many cha nnels have become over-wide or deep. The impact is seen in the literature to be manifested largely through the Factors Substrate/Siltation, and Velocity/Depth/Levels. There is little quantitative work on the dimensions of channels preferred by Ranunculus. Over-wide channels and consequent reductions in velocity are cited as having a detrimental impact on Ranunculus. There was little reference in the literature to gradient, a natural influence on velocity, that is greatly modified locally by sluices etc. A much greater emphasis is placed on phosphate than nitrate in the literature. It is suggested that phosphorus is a fundamental influence on riverine macrophyte communities and may set the underlying potential for impact to which other factors contribut e. The impact of phosphorus on Ranunculus is highly confounded by other environmental factors. It is frequently observed that the dominant macrophyte of Chalk rivers, Ranunculus penicillatus subsp. pseudofluitans, is generally found in fast flowing conditions. It is R and D TECHNICAL REPORT W1- 042/TR vi presumably this observation which has led to so much rehabilitation work involving changing channel dimensions to increase velocity. Recently completed projects on the River Avon have seen Ranunculus returning and occupying most of the in-channel habitat. However, recent high flow conditions may be more responsible for the spectacular return of Ranunculus than the contributions made by the project design. Many of the rehabilitation projects did not have any systematic or comprehensive monitoring of the impact of the scheme. This has greatly reduced the potential value of these schemes to future management of Chalk rivers. It is recommended that in order for the Environment Agency to fulfil its responsibilities under the Chalk Streams Biodiversity Action Plan the status of Ranunculus on all listed Chalk rivers should be established as soon as possible. In view of the importance of discharge in determining good Ranunculus growth there is also a need to establish the relationship between discharge, physical dimensions, water quality and sediment loading. In addition, there is an urgent requirement, given future climate change, to predict what discharge is required in any one catchment, river or reach to conserve Ranunculus and the health of Chalk rivers in general. These investigations will be particularly helpful in establishing criteria for rehabilitation projects. Monitoring the impacts of rehabilitation projects will provide data for comparison with the original criteria. In many Chalk rivers Ranunculus is maintained at high levels by management practices which have favoured it over its competitors. There is a need to strive for management that is in the best interests of the whole of the Chalk river ecosystem. R and D TECHNICAL REPORT W 1-042/TR v ii ACKNOWLEDGEMENTS iv EXECUTIVE SUMMARY v CONTENTS 1.
Publisher: Environment Agency
Subject Keywords: Macrophyte; Database; Chalk streams; Water-crowfoot; Proforma; River keepers; Riparian owners; River rehabilitation; Favourable status
Taxonomic Keywords: Ranunculus
Extent: 122
Permalink: http://www.environmentdata.org/archive/ealit:4621
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