The importance of environmental heterogeneity in lotic ecosystems is well recognised in river management, and continues to underpin studies of hierarchical patch dynamics, geomorphology and landscape ecology.We evaluated how physical characteristics and water chemistry measurements at high spatiotemporal resolution defi ne channel units of potential ecological importance along 134 km of the lower Waikato River in North Island, New Zealand.We used multivariate hierarchical clustering to classify river reaches in an a priori unstructured manner based on (i) high-frequency, along-river water quality measurements collected in four seasons and (ii) river channel morphology data resolved from aerial photos for 1-km long reaches.Patterns of channel character were shaped by the depth and lateral complexity of constituent river reaches, while water quality patterns were represented by differences in clarity, chlorophyll fl uorescence and specifi c conductance driven by tributary infl ows in the mid-section of the river and tidal cycles in the lower section.Management units defi ned by physical characteristics or water quality did not necessarily align with boundaries typically refl ecting clinal processes (e.g.tidal infl uence) or geomorphic, network or anthropogenic discontinuities.The results highlight the dynamic spatial and temporal properties of large rivers and the need to defi ne clear objectives when deriving spatial units for management and research.Given that actions and targets for physical channel and water quality management may differ, the spatial extent identifi ed for each of these does not necessarily need to directly coincide, although both should be considered in decision making and experimental design.
Although every large river basin is unique, we identify 12 broadly applicable lessons related to integrated management which river basin managers should bear in mind. These are: the size of a river basin has an important infl uence on the complexities of management; decision makers tend to give priority to stakeholders seeking to gain short term personal benefi t; river basin managers often fail to learn from the experience of others, or even from past mistakes in their own river basin; preventing river basin degradation is far cheaper than repairing damage; a basin plan does not replace a basin planning process; basin plans and their implementation must strike an appropriate bal- ance between stakeholders; sound knowledge is essential in evidence-based decision making, but decisions are ultimately political and involve value judgments; technical work must be peer reviewed to ensure quality; the em- phasis on the fi shery in basin planning is often unrelated to the importance of the fi sh to human subsistence; asset- based management approaches are very complex in large river basins; large scale developments attract a lot of planning attention, but basins are often degraded through numerous small scale impacts.
Spatial and temporal changes in the water chemical parameters and chlorophyll-a concentration were investigated in Kulső-Beda oxbow-lake of the Danube and compared with that of the main channel in 2007-2008. The oxbow-lake water differed from that of the main arm with regards to concentrations of the C, N and P forms. The NO3 - -N, PO4 3- -P, TDN, TDP concentrations were remarkably lower, while the concentrations of DOC, TDC, TOC and of chlorophyll-a were higher in the oxbow-lake than in the main channel. The differences between the NO3 - -N and PO4 3- -P concentrations of the main arm and oxbow-lake decreased with increasing river discharge. The phytoplankton biomass signifi cantly correlated with the TP (r=0.90), NO3 - -N (r=-0.45) concentrations and TDN:TDP ratio (r=-0.47), NO3 - -N:PO4 3- -P ratio (r=-0.55), which suggested P limitation of phytoplankton growth. Signifi cant positive correlation was found between the chlorophyll-a and SPM, POC. The phytoplankton biomass negatively, while NO3 - -N concentration positively correlated with the water discharge of the main arm. The limno- logical characteristics of BDU were dependent on the water regime of the main channel.
