Terrestrial Retention Research Articles

Exploring dynamics of riverine phosphorus exports under future climate change using a process-based catchment model

A quantitative understanding of riverine phosphorus (P) export in response to shifts in anthropogenic inputs, terrestrial retention, and climate is important for developing mitigation measures at a watershed scale. In this study, we simulated a decadal change in the riverine P export in a human-dominated watershed from a cold climatic region located in Northeast Asia. A process-based catchment model nested within a delicate land P module was applied to simulate the dynamics of P retentions and its exports in the watershed. We found that the terrestrial P retention capacities declined for 2008–2017, and the decline rates would accelerate under three representative concentration pathways (i.e. RCP2.6, RCP4.5 and RCP8.5). The P released from the diffused source and historical legacy could partly offset the effort through point-source P reduction by the improved wastewater treatments. Climate changes (e.g., duration and frequency of extreme rainfall event) could accelerate P deliveries from the P legacy retained in soils. We suggest that a long-term watershed P management strategy should be targeted to reduce historical P legacy input into river rather than solely focusing on the short-term changes in the riverine P concentration.

The slow and steady salinization of Sparkling Lake, Wisconsin

The concentrations of conservative solutes in seepage lakes are determined by the relative inputs of precipitation vs. groundwater. In areas of road salt application, seepage lakes may be at high risk of salinization depending on groundwater flow. Here, we revisit a 1992 analysis on the salinization of Sparkling Lake, a deep seepage lake in Northern Wisconsin. The original analysis predicted a rapid increase in chloride concentrations before reaching a steady steady of 8 mg L−1 by 2020. Forty years of monitoring Sparkling Lake show that rather than reaching a dynamic equilibrium, chloride concentrations have steadily increased. We update the original box model approach by adding a soil reservoir component that shows the slow steady rise in chloride is the result of terrestrial retention. For freshwater rivers and lakes, chloride retention on the landscape will both delay chloride impairment and prolong recovery and must be considered when modeling future chloride contamination risk.

Assessing N emissions in surface water at the national level: Comparison of country-wide vs. regionalized models

Many countries are developing models to estimate N emissions in rivers as part of national-scale water quality assessments. Generally, models are applied with national databases, while at the regional scale, more detailed databases are sometimes available. This paper discusses pros and cons of developing regionalized models versus applying countrywide models. A case study is used to support the discussion. The model used, called Nutting-N (NUTrient Transfer modelING-Nitrogen), relies on a statistical approach linking nitrogen sources and watershed land and river characteristics and aims to evaluate the risk of water bodies failing to reach quality objectives defined by national and federal policies. After calibration and evaluation at the national scale (France), the predictive quality of the model was compared with two regionalized models in a crystalline massif (Brittany, western France, 27,000km2) and in a sedimentary basin (Seine, Paris basin, 78,000km2), where detailed regional databases are available. The national-scale model provided robust predictions in most conditions encountered in France (efficiency=0.69). Terrestrial retention was related mainly to specific runoff, and its median value was estimated at 49% of the N surplus, whereas median river retention represented 18% of incoming N discharge. Regionalizing the model generally improved goodness-of-fit, as the root mean squared error was reduced by 6–24%. However, precision of parameter estimates degraded when too few monitoring basins were available or when variability in land and river characteristics was too low in the calibration dataset. Hence, regional-scale models should be advocated only after the trade-off between improvement of fit and degradation of parameter estimates is examined.

Inorganic nitrogen retention in acid‐sensitive lakes in southern Norway and southern Ontario, Canada—a comparison of mass balance data with an empirical N retention model

AbstractIn‐lake retention of inorganic nitrogen species (nitrate and ammonium) was estimated from mass balances in five acid‐sensitive lakes in southern Norway and eight in southern Ontario, Canada, to evaluate an empirical in‐lake N retention (RN) model. This model is included in the First‐order Acidity Balance (FAB) model, which currently is used for calculation of critical acid loads and exceedances in many countries. To estimate in‐lake RN, the FAB model uses a recommended mass transfer coefficient (SN) of 5 m year−1, which mainly is derived from NO3− mass balances in Canadian lakes. To date, the in‐lake RN model has not been evaluated for large parts of Europe. At the Norwegian study sites receiving the highest N deposition (>120 meq m−2 year−1) the net in‐lake retention of inorganic N (TIN) exceeded the corresponding terrestrial retention by a factor of 1·1–2·6. Despite differences in N loading and hydrology at the Norwegian and Canadian sites, both the mean mass transfer coefficients for NO3− (SNO3; 6·5 versus 5·6 m year−1) and TIN (STIN; 7·9 versus 7·0 m year−1) were of comparable magnitude. Both mean values and ranges of SNO3 suggest that the default SN value presently recommended for FAB model applications seems valid over a large range in N inputs and areal water loads (qs). However, owing to the relatively few data available for lakes with high qs values (15–150 m year−1), it is recommended that more lakes within this range be included in future studies to obtain a more precise prediction of in‐lake N retention over a wide qs gradient. Also, when considering that the FAB model treats all inorganic N leaching from a catchment as NO3−, it seems reasonable to use a default STIN value instead of just SNO3 when estimating in‐lake RN. In that case, the in‐lake RN presently calculated by the FAB model might be slightly underestimated. Copyright © 2003 John Wiley & Sons, Ltd.

Yields of Dissolved Organic C, N, and P. from Three High-Elevation Catchments, Colorado Front Range, U.S.A.

Ecosystem dynamics in high-elevation watersheds are extremely sensitive to changes in chemical, energy, and water fluxes. Here we report information on yields of dissolved organic C, N, and P for the 1999 snowmelt runoff season from three high-elevation catchments in the Colorado Front Range, U.S.A.: Green Lake 4 (GL4) and Albion townsite (ALB) on North Boulder Creek and the Saddle Stream (SS), a tributary catchment dominated by alpine tundra. Dissolved organic carbon (DOC) concentrations in stream waters ranged from <1 to 10 mg C L-1, with the highest values occurring at the SS site. Dissolved organic nitrogen (DON) concentrations ranged from below detection limits to 0.28 mg N L-1 and were again highest at the tundra-dominatedsite. Dissolved organic phosphorus (DOP) concentrations were at or near detection limits throughout the season in all three catchments indicating a strong terrestrial retention of P. OnlyDOC showed a significant relationship to discharge. Yields of DOC in the three catchments ranged from 10.6 to 11.8 kg C ha-1 while yields of DON and DOP ranged from 0.32 to 0.41 and 0.02 to 0.08 kg ha-1, respectively. The relatively highyield of organic N and P relative to C from the highest elevationsite (GL4) was somewhat surprising and points to either: (1) a source of dissolved organic material (DOM) in the upper reaches of the catchment that is enriched in these nutrients or (2) theselective uptake and processing of organic N and P downstream ofthe sampling site. Additionally, seasonal changes in the relativeimportance of DOM precursor materials appear to result in changesin the N content of DOM at both the GL4 and ALB sites.

Heavy metal budgets for two headwater forested catchments in background areas of Finland

Mean annual (1994–1996) budgets for Cd, Cu, Ni, Pb and Zn at two background, forested catchments, VK and HJ, in Finland are presented. Budgets for plots (VK3, HJ1 and HJ4) included throughfall (TF), litterfall (LF) and soil leaching fluxes, and for catchments terrestrial retention and leaching and lake sedimentation fluxes. Total deposition (TD) loads were relatively low (Cd<0.1, Cu<2, Ni<1, Pb<3 and Zn<5 mg m −2 year −1) and that even in these areas almost half of the TD was in the form of dry deposition. Retention of TD within catchments was ⩾77% for all metals, except for Ni at VK (54%). For Cu and Pb, the retention was 94–97%. Most of the retention (74–97%) took place in the terrestrial part of the catchment, lake sedimentation accounting for the remainder. Plot-scale soil leaching fluxes at 40 cm of Cd, Cu (VK3) and Ni (VK3) were greater (⩾100%) than TD inputs. Most of the catchment retention must therefore have taken place either deeper in the soil or in the lowland peatland areas. The humus layer was particularly effective in retaining Cu and Cd (65–81% and 51–78% of total inputs to the forest floor (TF+LF)). The retention of Pb by the humus layer was less than expected (26–54% of TF+LF). Litterfall was a particularly important internal flux for Zn.

Ion Mass Budgets for Lakes in the Turkey Lakes Watershed, June 1981 – May 1983

Ion mass budgets were determined for two water years (June – May 1981–83) for Batchawana L. South, Wishart L., Little Turkey L., and Turkey L. Water budgets balance within measurement error except for Little Turkey L. (output surplus for both water years) and Batchawana L. South (output surplus for 1982–83). Groundwater seepage is hypothesized to explain these water budget imbalances. The chemical budgets show that H+, NH4+, and NO3− are retained by the lakes to varying degrees. The major input pathway for H+ and NH4+ is via direct atmospheric deposition, while relatively weaker terrestrial retention of NO3− causes basin runoff to be the major input pathway for this parameter. All three species are playing an acidifying role on the Turkey Lakes Watershed. Chemical budgets for Mg2+, Na+, K+, SO42−, and Cl− are generally balanced for all lakes relative to the water budgets. In contrast, Ca2+ and acid-neutralizing capacity (ANC) exhibit excess output over measured plus estimated inputs. Probable unmeasured inputs of these two parameters include groundwater seepage and Ca2+ exchange with the sediments. In-lake generation of ANC by SO42− reduction is of minor importance.

Variation in trace metal exports from small Canadian shield watersheds

Annual exports of Cu, Pb, and Cd were estimated for eleven headwater and two lake outflow streams in the District of Muskoka, Ontario, Canada. COCl2-APDC coprecipitation coupled with anodic stripping voltammetry was used to determine metal concentrations. Concentrations of all three metals were similar to those reported from other temperate forested ecosystems, being usually less than 1 ug L−1 with Cd undetectable (<25 ng L−1) in many samples. There was limited evidence for a spring peak in metal concentrations associated with the snowpack melt. Annual export (mass per unit area per year) of each metal was calculated; variability between streams was small. Exports of Pb appear to be related to the organic content of the water. Copper export was correlated with watershed area, not with organic acids, implying that a different transport mechanism and possibly a different source are important for this metal. The exports of Pb and Cu were much lower in all streams than the estimated annual atmospheric metal depositions reported for this area in the literature. Terrestrial retention was higher than 95% for all catchments, while lake retention was slightly lower in some cases. Despite the small fractional loss of trace metal from the watersheds, terrestrial inputs can comprise a significant portion of the total metal load to typical lakes in this region because of size of the catchments relative to the lake areas.

An examination of the relationship between drainage basin morphology and the export of phosphorus1

The relationship between phosphorus export and several morphologic parameters was examined for 18 forested drainage basins underlain by igneous bedrock. A regression model (r = 0.94) relating phosphorus export to the length of stream per unit area (drainage density) is presented: urn:x-wiley:00243590:media:lno19752020267:lno19752020267-math-0001 A hypothesis based on terrestrial retention of phosphorus and baseflow is proposed to explain the relationship.