Efficiency and dimensioning of riparian buffer zones in agricultural catchments

A strong linear correlation was found between the log-transformed load and retention of nitrogen and phosphorus in riparian buffer zones (r=0.99 and 0.997, respectively). Analyses of N and P budgets in four riparian forests of varying age (two grey alder stands in Estonia and two riparian deciduous forests in USA) show a significant efficiency. Despite the different input load (72.9–110.4 kg N ha⁻¹ year⁻¹ and 2.5–3.0 kg P ha⁻¹ year⁻¹), the outputs into streams from the alder stands systems were comparably low (9.0–13.2 and 0.38–0.62 kg ha⁻¹ year⁻¹). The older forests from the USA showed less efficiency. Plant uptake of both N and P in younger stands was significantly higher than in older forests. Methods to determine the buffer zones' and buffer strips' width and their efficiency are presented. The testing of efficiency assessment in a watershed in Estonia demonstrated an expected efficiency of buffers.     

Nutrient runoff dynamics in a rural catchment: Influence of land-use changes, climatic fluctuations and ecotechnological measures

The main trend in land-use changes in the Porijõgi River catchment, south Estonia, is a significant increase in abandoned lands (from 1.7% in 1987 to 10.5% in 1997), and a decrease in arable lands (from 41.8 to 23.9%). Significant climatic fluctuations occurred during the last decades. Milder winters (increase of air temperature in February from −7.9 to −5.5°C during the period 1950–1997) and a change in the precipitation pattern have influenced the mean annual water discharge. This results in more intensive material flow during colder seasons and decreased water runoff in summer. During the period 1987–1997 the runoff of total-N, total-P, SO₄, and organic material (after BOD₅) decreased from 25.9 to 5.1, from 0.32 to 0.13, from 78 to 48, and from 7.4 to 3.5 kg ha⁻¹ year⁻¹, respectively. Most significant was a 4–20-fold decrease in agricultural subcatchments while in the forested upper-course catchment the changes were insignificant. Variations of total-N, and total-P runoff in both the entire catchment and its agricultural subcatchments are well described by the change of land use (including fertilization intensity), soil parameters and water discharge. In small agricultural subcatchments the rate of fertilization was found to be the most important factor affecting nitrogen runoff, while land-use pattern plays the main role in larger mosaic catchments. Ecotechnological measures (e.g. riparian buffer zones and buffer strips, constructed wetlands) to control nutrient flows from agricultural catchments are very important.     

Nitrogen dynamics of storm runoff in the riparian zone of a forested watershed

The influence of storm runoff processes on stream nitrogen dynamics was investigated in a headwater riparian swamp on the Oak Ridges moraine in southern Ontario. Hydrologic data were combined with analysis of an isotopic tracer (¹⁸0) and nitrogen (NH ₄ ⁺ , NO ₃ ^– ) concentrations in saturation overland flow and stream discharge. Storm runoff was separated into its event and pre-event components using¹⁸O in order to examine the effect of water source on nitrogen chemistry. Laboratory experiments were also used to study nitrogen transformation associated with storm runoff-surface substrate interactions in the swamp. In most storms N0₃-N and NH₄-N concentrations in the initial 3–4 mm throughfall increment were 10–20x and 20–100x higher respectively than stream base flow concentrations. Maximum stream N0₃-N concentrations were < 2x to 6x higher than base flow concentrations and preceded or coincided with peak stream discharge. Storm-to-storm variations in stream N0₃-N behaviour also occurred during the hydrograph recession phase. NH₄-N concentrations attained an initial peak on the rising hydrograph limb, or at peak stream discharge. A second NH₄-N increase occurred during the late recession phase 3–5 h after maximum stream discharge. Inorganic-N concentrations in surface runoff were similar to peak streamflow.The close agreement between observed N0₃-N concentrations and values predicted from a chemical mixing model indicate that stream N0₃-N variations were controlled mainly by the mixture of throughfall and groundwater in surface stormflow from the swamp. Laboratory experiments also indicated that N0₃-N in surface runoff behaved conservatively when mixed with swamp substrates. With the exception of the late hydrograph recession phase, observed stream NH₄-N concentrations were much lower than concentrations predicted by the chemical mixing model. The rapid loss of NH₄-N from mixtures of surface stormflow and swamp substrates in laboratory experiments and the absence of uptake in sterilized substrates indicated that NH₄-N retention in surface storm runoff was due to biotic processes.     

Nitrogen and phosphorus budgets for the sub-tropical Richmond River catchment, Australia

Nitrogen and phosphorus budgets were developed forfour sub-catchments in the Richmond River catchmentfor two study years. The catchment is used for avariety of farming pursuits including dairying, beef,cropping, fruit, nuts, forestry, and sugar cane. Eachsub-catchment varies in hydrology, the proportion ofeach land use, and the population density whichenabled a unique opportunity to study fluxes andstorage associated with a variety of environmentalfactors. Total loadings entering each sub-catchmentvaried from 12 to 57 kg ha^–1yr^–1 fornitrogen and 0.25 to 6.6 kg ha^–1yr^–1 forphosphorus with little inter-annual variation.Averaged across the whole catchment, nitrogen fixation(47%) dominated the inputs; fertiliser (26%) andrainfall (21%) made up the next largest inputs.Fertiliser inputs dominated the phosphorus budget(65.5%); rainfall and manures making up 13% and 12%respectively. Produce dominated the outputs of bothnitrogen and phosphorus from the four sub-catchmentsbeing greater than the riverine export. The deliveryof nitrogen to catchment streams ranged from <1 to24% of the total inputs and the delivery of phosphorus to catchment streams ranged from <1 to 39%. Storage of phosphorus in catchment soils varied between –0.32 and 4.46 kg ha^–1yr^–1. Whendenitrification and volatilisation were estimated using data from other studies, storage of nitrogen ranged from 1 to 24 kg ha^–1yr^–1. Despite theepisodic nature of runoff in the sub-tropical RichmondRiver catchment, the magnitude of nutrient fluxes andstorage appear similar to other catchments of theworld which have mixed land use and relatively lowcatchment nutrient loadings.     

Comparison between biological and chemical treatment of wastewater containing nitrogen and phosphorus

The present work compared chemical and biological treatment methods to achieve the most efficient treatment for the reduction or elimination of phosphorus and nitrogen from mixed industrial–domestic wastewaters. Batch chemical precipitation by ferric chloride and aluminum sulfate (alum) and a continuous biological suspended growth system were investigated as well as the optimum operating conditions. Concerning chemical treatment, Alum generally achieved a higher removal efficiency percentage for the investigated pollutants compared with FeCl₃ at their optimum pH and dose, especially with chemical oxygen demand (COD). FeCl₃ treatment achieved success only with phosphorus removal, while none of the COD, 5-day biochemical oxygen demand (BOD₅), total nitrogen (TN) and N–NH₃ achieved acceptable treatment and remained above the maximum permissible limits (MPL). Thus, for such wastewaters, alum is more efficient than FeCl₃. Biological treatment exhibited higher efficiencies, particularly towards nitrogen. TN removal increased by increasing the flow rate to 30–60 l/day. N–NH₃ removal was effective at the slowest flow rate and decreased with increasing flow rate, while an opposite trend was recorded for N–NO₃. At all flow rates, phosphorus levels were below the accepted MPL for discharging into natural systems. Moreover, there was a general trend for the proposed biological treatment to achieve a high removal efficiency for BOD₅ and COD, bringing them to acceptable levels to be released into watercourses safely, especially at the slowest flow rates. Thus, integration between the proposed chemical and biological treatment is highly recommended, producing high-quality effluents acceptable by the environmental law.     

Role of organophosphates in adaptations of an obligate water-breathing teleost (Tilapia nilotica L.) to hypoxia

Dry matter, total carbon (C), nitrogen (N) and phosphorus (P) content of mature bream from Lake Balaton were investigated and the quantities of N and P stored in the bream population and their possible removal by fishery were estimated. Carbon made up 43.3–44.8% of dry weight, N made up on average 10.6% of the dry weight of bream and P accounted for a further 2.7%. About 3.3 kg N ha^–1 and 0.9 kg P ha^–l are stored in the bream population. Approximately 0.5 kg N ha^–1 and 0.1 kg P ha^–1 are removed from the lake by bream harvest. Taking into account the total fish yield, the N removal is 2.1% and P removal 3.4% of the amount entering the lake.     

Phosphorus removal from agricultural runoff by constructed wetland

A free-water surface wetland covering an area of 2800 m² was operated from March 2002 to June 2004 for agricultural runoff treatment in the Dianchi Valley in China. In the wetland were grown Zizania Caduciflora Turez Hand-mazt and Phragmites australis (Cav.) Trin.ex Steud. The instantaneous inflow rate was measured and the integrated flux was recorded by an ultrasonic flow instrument all year round. The average inflow rate, hydraulic loading rate (HLR) and hydraulic retention time (HRT) were kept at 242 m³ d^?1, 12.7 cm d^?1 and 2.0 d, respectively. The annual average total phosphorus (TP) in the inflow was 0.87 mg L^?1, and the corresponding removal efficiency was calculated to be 59.0%. Biannual plant uptake and removal by harvesting and seed transport was the main pathway for TP removal, while the influent TP load was 12.9 g m^?2 year^?1. Hydraulic retention time had a significant positive correlation with the removal of P (r² = 0.88). Water temperature, inflow phosphorus load, inflow and hydraulic load rates were positively correlated with the removal of P. Inflow phosphorus concentrations were negatively correlated with the removal of P. It is shown that the free-water surface wetland was an effective and economical system for agricultural runoff treatment in lake regions.     

Spatial and temporal dynamics of mercury in Precambrian Shield upland runoff

Methylated and total Hg, and TOC concentrations were measured in precipitation and runoff in a first order Precambrian Shield watershed, and in precipitation, throughfall, shallow groundwater and runoff in a zero Precambrian Shield watershed. Plots dominated by open lichen-covered bedrock and another containing small patches of conifer forest and thin discontinuous surficial deposits were monitored within the zero order catchment. Methyl (3–10 fold) and non-methyl (1.4–2.8 fold) Hg concentrations changed irregularly during rainfall and snowmelt runoff events in all catchments. Temporal patterns of Hg concentration in runoff included flushing and subsequent dilution as well as peak concentrations coinciding with peak or recession flow. Mercury export was highest from lichen-covered bedrock surfaces as a result of high runoff yields and minimal opportunity for physical retention and in the case of MeHg demethylation. Forest canopy and lichen/bedrock surfaces were often net sources for Hg while forest soils were mostly sinks. However, upland soils undergoing periodic reducing conditions appear to be sites for the in situ production of MeHg.     

Effect of basic operating parameters on biological phosphorus removal in a continuous-flow anaerobic–anoxic activated sludge system

A continuous-flow anaerobic–anoxic (A2) activated sludge system was operated for efficient enhanced biological phosphorus removal (EBPR). Because of the system configuration with no aeration zones, phosphorus (P) uptake takes place solely under anoxic conditions with simultaneous denitrification. Basic operating conditions, namely biomass concentration, influent carbon to phosphorus ratio and anaerobic retention time were chosen as variables in order to assess their impact on the system performance. The experimental results indicated that maintenance of biomass concentration above 2,500 mg MLVSS/L resulted in the complete phosphate removal from the influent (i.e. 15 mg PO₄ ³⁻-P/L) for a mean hydraulic residence time (HRT) of 15 h. Additionally, by increasing the influent COD/P ratio from 10 to 20 g/g, the system P removal efficiency was improved although the experimental results indicated a possible enhancement of the competition between phosphorus accumulating organisms (PAOs) and other microbial populations without phosphorus uptake ability. Moreover, because of the use of acetate (i.e. easily biodegradable substrate) as the sole carbon source in the system feed, application of anaerobic retention times greater than 2 h resulted in no significant release of additional P in the anaerobic zone and no further amelioration of the system P removal efficiency. The application of anoxic P removal resulted in more than 50% reduction of the organic carbon necessitated for nitrogen and phosphorus removal when compared to a conventional EBPR system incorporating aerobic phosphorus removal.     

Purification of nitrate-rich agricultural runoff by a hydroponic system

The purification of nitrate-rich agricultural runoff by a floating-raft (FR) hydroponic system was investigated at 3-, 2- and 1-d hydraulic retention times (HRTs) with particular emphasis on nitrogen conversion and removal through the system. The FR system has a dissolved oxygen (DO) environment similar to the horizontal subsurface flow system, generally 0.00mgL(-1), that facilitates denitrification. An efficient nitrate-nitrite-nitrogen (NO(x)-N) removal, 91%, 97% and 71% on average at 3-, 2- and 1-d HRT, respectively, was frequently achieved. The mean retentions were 17-47% for chemical oxygen demand, 31-64% for total nitrogen, and 8-15% for total phosphorus for the FR system. Mass balance analysis implied that the detectable DO concentration in the reactor, as low as 0.7mgL(-1), played a very important role in the conversion and removal of NH(3)-N and NO(x)-N, which finally affected the NO(x)-N removal at 3-d HRT.     

Incomplete mixing of limed water and acidic runoff restricts recruitment of lake spawning brown trout in Hovvatn, southern Norway

Repeated liming of Hovvatn during the 1981–1995 period assured successful reintroduction of lake spawning brown trout, Salmo trutta. Poor natural recruitment to the population was associated with low survival during early life stages (before hatching) as shown by the 0.5, 3.5, 0.9 and 1.0% of live embryos found in natural redds during the 1992–1995 period, respectively. The low survival was most likely caused by the combination of shallow spawning areas (<2.0 m) and acidic runoff (pH 4.0–4.8) which overlayed the limed part of the water body during the ice covered period. It is therefore concluded that this type of episodic acidification poses a major threat to lake spawning salmonids, and that it can retard or inhibit biotic recovery towards preacidified conditions expected as a result of liming. Addition of limestone gravel (8–32 mm) onto spawning grounds was an efficient alternative liming strategy as 33–36% live embryos were found in this substrate. Conversely, the trout actively avoided additions of shellsand, a behaviour most likely caused by the small particle size of shellsand (3–7 mm) relative to natural spawning gravel.     

Study of operational conditions of simultaneous nitrification and denitrification in a Carrousel oxidation ditch for domestic wastewater treatment

The study on the operational conditions of simultaneous nitrification and denitrification (SND) in the channel of oxidation ditch (OD) without the need for a special anoxic tank was carried out based on lab-scale and pilot-scale experiments using real domestic wastewater. The influence of sludge loading and component proportion in influent, temperature, hydraulic retention time (HRT), dissolved oxygen (DO) and operational mode on SND was investigated. The result indicated that the optimal DO (ODO) of SND occurrence was confirmed majorly by the sludge loading of influent and temperature, the high TCOD/NH₃–N and short HRT can enhance the occurrence of SND. A new operational mode was proposed that achieved a higher removal efficiency of 60–70% for total nitrogen by SND with HRT of 4–6 h, and the concentrations of NH₃–N and TN in effluent are less than 5 and 15 mg/L, respectively.     

Dynamics of nitrogen and phosphorus retention during wetland ecosystem succession

We compared the mechanisms of nitrogen (N) and phosphorus (P) removal in four young (<15 years old) constructed estuarine marshes with paired mature natural marshes to determine how nutrient retention changes during wetland ecosystem succession. In constructed wetlands, N retention begins as soon as emergent vegetation becomes established and soil organic matter starts to accumulate, which is usually within the first 1–3 years. Accumulation of organic carbon in the soil sets the stage for denitrification which, after 5–10 years, removes approximately the same amount of N as accumulating organic matter, 5–10 g/m²/yr each, under conditions of low N loadings. Under high N loadings, the amount of N stored in accumulating organic matter doubles while N removal from denitrification may increase by an order of magnitude or more. Both organic N accumulation and denitrification provide for long-term reliable N removal regardless of N loading rates. Phosphorus removal, on the other hand, is greatest during the first 1–3 years of succession when sediment deposition and sorption/precipitation of P are greatest. During this time, constructed marshes may retain from 3 g P/m²/yr under low P loadings to as much as 30 g P/m²/yr under high loadings. However, as sedimentation decreases and sorption sites become saturated, P retention decreases to levels supported by organic P accumulation (1–2 g P/m²/yr) and sorption/precipitation with incoming aqueous and particulate Fe, Al and Ca. Phosphorus cycling in wetlands differs from forest and other terrestrial ecosystems in that conservation of P is greatest during the early years of succession, not during the middle or late stages. Conservation of P by wetlands is largely regulated by geochemical processes (sorption, precipitation) which operate independently of succession. In contrast, the conservation of N is controlled by biological processes (organic matter accumulation, denitrification) that change as succession proceeds.     

Nutrient losses in runoff from grasslandand shrubland habitats in southern New Mexico: II. Field plots

Losses of dissolved nutrients (N, P, K, Ca, Mg, Na,Cl, and SO₄) in runoff were measured on grasslandand shrubland plots in the Chihuahuan desert ofsouthern New Mexico. Runoff began at a lowerthreshold of rainfall in shrublands than ingrasslands, and the runoff coefficient averaged 18.6%in shrubland plots over a 7-year period. In contrast,grassland plots lost 5.0 to 6.3% of incidentprecipitation in runoff during a 5.5-year period. Nutrient losses from shrubland plots were greater thanfrom grassland plots, with nitrogen losses averaging0.33 kg ha^–1 yr^–1 vs0.15 kg ha^–1 yr^–1, respectively, during a 3-year period. Thegreater nutrient losses in shrublands were due tohigher runoff, rather than higher nutrientconcentrations in runoff. In spite of these nutrientlosses in runoff, all plots showed net accumulationsof most elements due to inputs from atmosphericdeposition. Therefore, loss of soil nutrients byhillslope runoff cannot, by itself, account for thedepletion of soil fertility associated withdesertification in the Chihuahuan desert.     

Retention of nitrogen, phosphorus and silicon in a large semi-arid riverine lake system

Lakes and reservoirs (impoundments) are often viewed as a sink for nutrients within the river continuum. To date, most studies on nutrient retention within impoundments are derived from the temperate climate zones of Europe and North America, only consider one nutrient, and are often short-term (1–2 years). Here, we present a long-term (17 year) data set and nutrient (nitrogen, phosphorus and silica) budget for two connected semi-arid lakes (the Lower Lakes) at the terminus of the River Murray, Australia. Most of the filterable reactive phosphorus and nitrate entering the lakes were retained (77 and 92%, respectively). Total phosphorus (TP) was also strongly retained (55% of the annual TP load on average) and the annual TP retention rates could be predicted as a function of the areal hydraulic loading rate (annual lake outflow/lake surface area). On average, there was a slight net retention (7%) of the annual total nitrogen (TN) load but a slight net export (6% of the load) of organic N. TN retention as function of the areal hydraulic loading rate was lower than expected from existing models, possibly because of high nitrogen fixation rates in the Lower Lakes. Silica was retained (39%) at similar rates to those observed in previous studies. There was also a marked increase in the TN:TP and TN:Si ratios within the lake (TN:TP~30 and TN:Si~0.67) compared to those entering (TN:TP~15, TN:Si~0.45), as a consequence of the relatively low net retention of nitrogen.     

Control of phosphorus discharges: present situation and trends

The dominating sources of phosphorus in municipal wastewaters are excreta, 1.4 g P/(cap.d) and detergents, 0.6 – 2 g P/(cap.d). Detergent phosphorus can be substituted by nitrilotriacetic acid or zeolites, but if a substantial reduction of phosphorus in municipal waters is to be achieved, modifying the treatment process is necessary. Primary, treatment by sedimentation removes only 10–15% and secondary biological treatment 20–30% of the phosphorus in waste water. If chemicals are added to the primary or secondary treatment stage or to a separate chemical stage, phosphorus can be efficiently removed. An effluent level of 0.8–1.5 g P m^-3 is easily achieved and with a filtration step it is possible to maintain 0.2 g P m^-3 in the effluent. Different process configurations are discussed. As precipitants, ferrous and ferric salts, alum and lime are widely used. By introducing anaerobic zones in the activated sludge process, it is possible to promote the growth of bacteria which enhance biological phosphorus uptake. This makes it possible to achieve high phosphorus removal without or, al least, with very small chemical additions. Several emerging physical, chemical and biological phosphorus removal processes are discussed. The removal of phosphorus to a level of 0.8–1.5 g P m^-3 increases cost 10–20% compared with conventional primary secondary treatment. Higher removal efficiencies will rapidly increase the marginal cost per marginal kg P removed.     

Phosphorus retention in lab and field-scale subsurface-flow wetlands treating plant nursery runoff

Constructed wetland systems built to handle nutrient contaminants are often efficient at removing nitrogen, but ineffective at reducing phosphorus (P) loads. Incorporating a clay-based substrate can enhance P removal in subsurface-flow constructed wetland systems. We evaluated the potential of crushed brick, a recycled building product, and two particle sizes of a palygorskite–bentonite industrial mineral aggregate (calcined clay) to sorb P from simulated nutrient-rich plant nursery effluent. The three substrates were screened for P sorbing behavior using sorption, desorption, and equilibration experiments. We selected one substrate to evaluate in an 8-month field trial to compare field sorption capacity with laboratory sorption capacity. In the laboratory, coarse calcined clay average sorption capacity was 497 mg kg⁻¹ and it sorbed the highest percentage of P supplied (76%), except at exposure concentrations >100 mg L⁻¹ where the increased surface area of fine calcined clay augmented its P sorption capacity. Subsurface-flow mesocosms were filled with coarse calcined clay and exposed to a four and seven day hydraulic retention time treatment. Phosphorus export was reduced by 60 to 74% for both treatments until substrate P-binding sites began to saturate during month seven. During the eight month experiment, the four and seven day treatments fixed 1273 ± 22 mg kg⁻¹ P and 937 ± 16 mg kg⁻¹ P, respectively. Sequential extractions of the P saturated clay indicated that P could desorb slowly over time from various pools within the calcined clay; thus, if the calcined clay were recycled as a soil amendment, most P released would be slowly available for plant uptake and use. This study demonstrated the viability of using coarse calcined clay as a root bed substrate in subsurface-flow treatment wetlands remediating phosphorus from plant nursery runoff.     

Phosphorus budget in the Marne Watershed (France): urban vs. diffuse sources,dissolved vs. particulate forms

We evaluated the P sources (point, diffuse), through a nested watershed approach investigating the Blaise (607 km²), dominated by livestock farming, the Grand Morin (1202 km²), dominated by crop farming, and the Marne (12,762 km²), influenced by both agriculture and urbanization. Fertilizers account for the main P inputs (>60%) to the soils. An agricultural P surplus (0.5–8 kg P ha^–1 year^–1) contributes to P enrichment of the soil. The downstream urbanized zone is dominated by point sources (60%, mainly in dissolved forms), whereas in the upstream basin diffuse sources dominate (60%, mostly particulate). Among the diffuse sources (losses by forests, drainage and runoff), losses by runoff clearly dominate (>90%). P retention in the alluvial plain and the reservoir represents 15–30% of the total P inputs. Dissolved and particulate P fluxes at the outlet of the Marne are similar (340 and 319 tons of P year^–1, respectively). The Blaise sub-basin receives P from point and diffuse sources in equal proportions, and retention is negligible. The Grand-Morin sub-basin, influenced by the urbanized zone receives, as does to the whole Marne basin, 60% of P inputs as point sources. The total particulate phosphorus in suspended sediments averaged 1.28 g P kg^–1, of which about 60% are inorganic and 40% organic P. Particulate phosphorus exchangeable in 1 week and 1 year (³²P isotopic method) accounts for between almost 26% and 54% of the particulate inorganic phosphorus in the suspended sediment and might represent an important source of dissolved P, possibly directly assimilated by the vegetation.     

Influence of nitrogen species (NH4 + and NO3 −) on the dynamics of P in water–sediment–Salvinia herzogii systems

Water – Salvinia herzogii – sediment systems were exposed to different phosphorus and nitrogen combinations in outdoor experiments. The aim was to estimate the amounts of P immobilized in macrophytes and sediments, as well as to elucidate whether or not the presence of N affects the retention of P. The following components were added: o-P, o-P + NH₄ ⁺, o-P + NO₃ ^– + NH₄ ⁺, o-P + NO₃ ^–. The concentration of nutrients was periodically determined throughout the experiment (28 days). The concentrations of P and N in plant tissues and sediments were determined at the beginning and the end of the experiment. Sequential extractions of P-fractions in sediment were performed using the EDTA method (Golterman, 1996). The removal efficiency of P in water was 95–99%. The removal of NH₄ ⁺ (97–98%) was more effective than that of NO₃ ^– (44–86%). The presence of nitrogen species increased the removal velocity of o-P from water, NH₄ ⁺ was the most effective species. Sediments not only had higher P removal rates than macrophytes but, in the control treatment without macrophytes, they reached the values obtained by macrophytes plus sediments in the other treatments. The adsorption of P takes place at the surface layer of the sediment (1 cm). Most of the P incorporated into the sediment during the experiment was sorbed by the fraction Fe(OOH)P. The addition of nutrients to water modified the leaves/lacinias weight ratio.     

赤红壤植蔗坡地坡面径流及溶解态氮磷流失特征

为探究南方高强度、高频次降雨下赤红壤区坡耕地土壤侵蚀及氮磷养分流失的特征,基于野外径流小区原位观测试验,通过测定自然降雨下赤红壤植蔗坡地坡面径流和溶解态氮磷流失量,探讨自然降雨下甘蔗种植对赤红壤坡面径流及溶解态氮磷流失的影响。结果表明：(1)2019年和2020年,径流量分别为1111.3 m~3/hm~2和3269.4 m~3/hm~2,硝态氮(NO~-₃-N)流失量分别为1.39 kg/hm~2和15.60 kg/hm~2,铵态氮(NH~+₄-N)流失量分别为0.37 kg/hm~2和1.02 kg/hm~2,可溶性磷流失量分别为0.20 kg/hm~2和0.27 kg/hm~2。2019年和2020年植蔗坡地径流及溶解态氮磷流失量均集中在6月份,占流失总量的45%以上,硝态氮(NO~-₃-N)是径流氮素流失的主要形式,占79%以上。此外,2019年和2020年5月至8月,侵蚀性降雨场次分别为18次和23次,侵蚀性降雨量分别为407.8 mm和668.0 mm。(2)不同侵蚀性降雨条件下,植蔗坡地溶解态氮磷流失量及其...