CN105136691A - Determination method of release amount of nitrogen and phosphorus pollutants in sediment - Google Patents

Abstract

The invention relates to a determination and calculating method of a release amount of nitrogen and phosphorus pollutants in sediment. Through analysis of migration and transformation characteristics of parameters such as pollutant inlet/outlet total amount, deposition amount, degradation amount and atmospheric precipitation supplementary amount, based on the law of conservation of mass, a mass balance calculation model is built. Through the model, a release amount of nitrogen and phosphorus in polluted sediment of rivers and lakes in a region into water is calculated conveniently, and an annual release amount and a release rate of nitrogen and phosphorus pollutants in lake sediment are calculated so that macroscopic analysis of the total pollutant amount of lake water is realized. The conclusion produced by the method basically accords with objective law, is convenient to apply and can be widely used for analysis of main pollution structures of lakes at the present stage.

Description

A kind of assay method of Nitrogen In Sediment phosphor contaminant burst size

Technical field

The present invention relates to environmental monitoring technology field, be specifically related to a kind of assay method of pollutant burst size, particularly relate to a kind of assay method of Nitrogen In Sediment phosphor contaminant burst size.

Background technology

Bed mud refers to the sediment of rivers,lakes and seas, is the important component part of natural water area, is also the main accumulation place of various nutrients and pollutant in water body.Nutritive salt polluted bed mud is then deposit in bed mud after the nutrient such as nitrogen, phosphorus enters water body by all means, and major part year nutritive salt and water body keep mobile equilibrium, and after external source pollution obtains control, the nitrogen in water, phosphorus mainly may come from bed mud.

The method quantitatively calculating nitrogen Phosphurus release rule in the polluted bed mud of rivers and lakes at present mainly contains column core simulation, Interstitial Water concentration diffusion model estimation algorithm, the box method of original position, flume experiment method and mass balance method etc.

Wherein, Wen Wei etc. have carried out modeling effort to Haihe River substrate sludge nitrogen phosphorus nutrition thing static release, it is analyzing outer shroud river, Haihe River bridge (fresh water), full nitrogen (TN) in center bridge place water (close to seawater), organic in full phosphorus (TP) content and sediments, TN, on the basis of TP content, adopt column simulation reactor simulation to have studied static condition to plunge into the commercial sea bed mud N, P release rule is (see Wen Wei etc., Haihe River substrate sludge nitrogen phosphorus nutrition thing static release modeling effort, agro-environment science journal, 27th volume the 1st phase, 295-300 page, on January 20th, 2008).Model Cheng Xin etc. has carried out Simulation of Internal Loadings of Nitrogen And Phosphorus In A Lake, it is on the analysis foundations such as Luoma Lake sediment and Interstitial Water physico-chemical property, space distribution, under the constant temperature static condition that laboratory controls, simulate the sediment water interface nitrogen of soft Fu Ni district column core at Various Seasonal temperature, phosphorus exchange process (see Fan Chengxin etc., Simulation of Internal Loadings of Nitrogen And Phosphorus In A Lake, Oceanologia et Limnologia Sinica, the 33rd volume the 4th phase, 370-378 page, on July 30th, 2002).The employing such as Zhu Guangwei have studied small echo and lifts sand (wave height 8.77cm in wave flume, period of wave 0.8s) and large ripple lift sand (wave height 12.31cm and 13.29cm, period of wave 1.0s) Taihu Lake Sediment suspended and the action rule of N, P Nutrient release (see Zhu Guangwei etc., bottom mud in Taihu Lake in suspension Nutrient release wave flume experiment, lake science, 17th volume the 1st phase, 61-68 page, on March 5th, 2005).

At present, the environmental baseline that column core simulation is suitable for is many, simple to operate, cost is low, but but there is wall effect; Interstitial Water concentration diffusion model estimation algorithm, comparatively large by bioturbation and bed mud stability influence, need the Interstitial Water concentration gradient of degree of precision, and the diffusion parameter of form ion, application limitation is larger; The box method of original position, under long period of experiments, the environmental baselines such as EO, DO, pH are difficult to remain constant; In flume experiment, bed mud is difficult to maintain former state, and is subject to disturbing influence.Therefore, comparatively speaking, adopt mass balance method can reflect the release conditions of nitrogen and phosphorus pollutants more intuitively, especially when macroscopic calculation, by resolving the parameter Transport And Transformation features such as the turnover total amount of pollutant, deposition, degradation amount and atmospheric precipitation increment, set up nitrogen Phosphurus release amount and account model, endogenous pollution degree can be drawn comparatively easily, for the improvement of polluted bed mud and reparation provide technical research basis.

At present, Holland is the eutrophication problem in control Grevelingen lake, once utilizes mass budget model to carry out mass balance (see Kelderman to the total phosphorus of this Lake Water Body, P., Neth., J.Sea.Res., 14,229 (1980)), formula is as follows:

v _b·c _b+L·c _l·Δt+l·c _i·Δt+N·c _n·Δt

＝v _e·c _e+u·c _u·Δt+F·Δt

In formula, v _bc _bfor pondage (m at the beginning of the time period ³) and total phosphorus concentration (mg/L); Lc _lfor rainwash in the time period and wastewater flow rate (m ³/ d) and total phosphorus concentration; Lc _ifor entering the lake runoff water yield and total phosphorus concentration thereof in the time period; v _ec _efor time period Mo pondage and total phosphorus concentration thereof; Uc _ufor going out the lake runoff water yield and total phosphorus concentration thereof in the time period; F is the exchange capacity (kg) of sedimentary phosphate in the time period; Δ t is the time period chosen.

Utilize mass budget model (see Huang Shaoji etc. in China, the exchange that mass budget model calculates bottom mud in Taihu Lake phosphorus is put, environmental science, 13rd volume the 1st phase, 83-84 page, 1992) to calculate the burst size that Taihu Lake obtains annual sedimentary phosphate in 1980 be 205t, enter lake amount 240t the whole year a little less than exogenous phosphorus, account for and enter 46.2% of people Taihu Lake water body total phosphorus content the whole year; Wherein, total phosphorus concentration c in lake surface precipitation _n, be tried to achieve by (year precipitation total phosphorus content/annual precipitation); Enter the total phosphorus concentration c of lake runoff _i, be tried to achieve by (enter in year lake total phosphorus content-year precipitation total phosphorus content)/(enter in year lake total Water-year the total precipitation).

But, the method utilizing mass budget model to carry out calculating at present does not consider the sedimentation of pollutant in water body, release and the atmospheric precipitation supply situation to pollutant, is therefore necessary that a kind of novel polluted bed mud nitrogen Phosphurus release amount that can consider above-mentioned each factor of research accounts model.

Summary of the invention

The object of the present invention is to provide a kind of assay method of pollutant burst size, specifically provide a kind of assay method of Nitrogen In Sediment phosphor contaminant burst size.The present invention is by resolving the parameter Transport And Transformation features such as the turnover total amount of pollutant, deposition, degradation amount and atmospheric precipitation increment, based on law of conservation of mass, establish the mass budget model of macroscopic view, the nitrogen phosphorus of polluted bed mud in arealriver, lake is to water body contribution amount to adopt this model conveniently to draw, thus realizes the macroanalysis to total amount of pollutant formation in water body in lake.

For reaching this object, the present invention by the following technical solutions:

The invention provides a kind of assay method of Nitrogen In Sediment phosphor contaminant burst size, said method comprising the steps of:

(1) adopt the annual average water volume of flowmeter to river, lake of coming in and going out to measure, and adopt digest by potassium persulfate to measure pollutant total phosphorus concentration and adopt alkaline chitinase to clear up determined by ultraviolet spectrophotometry pollutant total nitrogen concentration to determine the average annual inlet W of pollutant rainwash _iquantum of output W average annual with pollutant rainwash _o;

(2) average annual rainfall volume R is determined to the average annual rainfall amount analysis in basin, place, river, lake;

(3) stratified sampling and Isotope Dating are carried out to determine the average annual hold-up S of pollutant in river, lake and bed mud deposition total amount P to lake bed mud in river, and draw the accumulation degradation coefficient K of pollutant;

(4) the total amount a of the nitrogen phosphorus that aquaculture produces is calculated;

(5) the average annual burst size of Nitrogen In Sediment phosphor contaminant is calculated according to formula (I) or formula (II):

$X=\frac{W_o+S+P}{1-K}-W_i-R---\left(I\right)$

X＝S-(R+W _i+a)×K(II)

Wherein, X is sediment pollution annual efflux (t); W _ifor the average annual inlet (t) of pollutant rainwash; W _ofor the average annual quantum of output (t) of pollutant rainwash; R is average annual rainfall volume (t); S is the average annual hold-up (t) of pollutant; P is bed mud deposition total amount (t); K is the accumulation degradation coefficient of pollutant; A is the total amount (t) of the nitrogen phosphorus that aquaculture produces.

The present invention adopts flowmeter to measure the average annual discrepancy amount in discrepancy river, lake, and unit is m ³/ s.Pollutant total phosphorus (TP) concentration adopts digest by potassium persulfate to measure, and unit is mg/L; Pollutant total nitrogen (TN) concentration adopts alkaline chitinase to clear up determined by ultraviolet spectrophotometry, and unit is mg/L.The digest by potassium persulfate wherein related to and alkaline chitinase are cleared up ultraviolet spectrophotometry and are this area common method, are not particularly limited.

In the present invention, the total amount a of the nitrogen phosphorus that aquaculture produces is according to " first time national Pollutant source investigation-culture fishery pollution source product discharge coefficient handbook ", by aquaculture amount in lake, and measuring and calculating discharge of major pollutant amount.In the present invention, the described average annual rainfall volume R of step (2) calculates according to formula (III):

R＝n·r·S·C _R·10 ^-3(III)

Wherein, n is polluted bed mud deposition year number (a); R is average annual rainfall amount (mm); S is the average annual hold-up (t) of pollutant; C _rfor pollutant levels in the rain.

Average annual rainfall amount in the present invention adopts rain gage bucket to measure, and unit is mm.Generally, local average annual rainfall data can be adopted when applying, data from water resource publication etc.

The present invention, by carrying out stratified sampling to bed mud, adopts the method for Isotope Dating, calculates polluted bed mud deposition year number.In the present invention, the average annual hold-up S of step (3) described pollutant calculates according to formula (IV):

$S={\stackrel{\‾}{C}}_w\·Q\×100---\left(IV\right)$

Wherein, for pollutant mean annual concentration (mg/L) in water body; Q is the volume or storage capacity (hundred million m that calculate water body ³).

In the present invention, step (3) described bed mud deposition total amount P calculates according to formula (V):

$P=C_p\·s\·h\·(1-\mathrm{\φ})\·\frac{\mathrm{\ρ}}{n}---\left(V\right)$

Wherein, C _pfor pollutants in sediments mean concentration (mg/kg); S is the bed mud area (km of whole water body ²); H is the polluted bed mud degree of depth (m); φ is water cut (%); ρ is bed mud unit dry weight (g/cm ³); N is polluted bed mud deposition year number (a).

In the present invention, the described accumulation degradation coefficient K of step (4) calculates according to formula (VI):

K＝exp(-k′Δt)(VI)

Wherein, K is accumulation degradation coefficient (nd ^-1); K ' is day degradation coefficient (d ^-1); Δ t is the sedimentation time that Isotope Dating draws, identical with bed mud sedimentation time.

In the present invention, described Isotope Dating is ²¹⁰pb determine year or ¹³⁷cs determines year.In sediment ²¹⁰pb, from two parts, a part be by ²²⁶ra decay also reaches with it mobile equilibrium ²¹⁰pb, a part is from the precipitum in air and the surplus that constantly decays of concentration ²¹⁰pb (is denoted as ²¹⁰pbex).

In the present invention, described in ²¹⁰pb determines to adopt constant recharge rate pattern (CRSmodel) to calculate average sedimentation rate in year.

Deposited the corresponding relation in time by the CRS model calculating acquisition bed mud degree of depth and bed mud, and can show by bed mud Isotope Dating result the rate of sedimentation measuring region.

As the preferred technical scheme of the present invention, the present invention adopts mass conservation measuring method, sets up formula as follows:

W _i-W _o＝S+U·K+D-X-R

Wherein: R=nrSC _r10 ^-3; u=R+X+W _i;

$P=C_p\·s\·h\·(1-\mathrm{\φ})\·\frac{\mathrm{\ρ}}{n};K=\exp (-k^{\′}\mathrm{\Δ}t)$

Arrangement formula draws:

$X=\frac{W_o+S+P}{1-K}-W_i-R$

Wherein, W _ifor the average annual inlet (t) of pollutant rainwash; W _ofor the average annual quantum of output (t) of pollutant rainwash; R is average annual rainfall volume (t); The average annual rainfall amount of r (mm); S is the bed mud area (km of whole water body ²); C _rfor pollutant levels in the rain; S is the average annual hold-up (t) of pollutant; for pollutant mean annual concentration (mg/L) in water body; Q is the volume or storage capacity (hundred million m that calculate water body ³); U is every year can for the total amount (t) of degradation of contaminant; K ' is degradation coefficient (d ^-1); P is certain year section bed mud deposition total amount (t); C _pfor pollutants in sediments mean concentration (mg/kg); H is the polluted bed mud degree of depth (m); φ is water cut (%); ρ is bed mud unit dry weight (g/cm ³); N is polluted bed mud deposition year number (a); X is pollutants in sediments annual efflux (t); Δ t is the sedimentation time (d) that Isotope Dating draws, identical with bed mud sedimentation time.

If only consider the waterpower swap time of water body in lake, then do not consider aqueous concentration (W _o) and bed mud deposition (P), formula is deformed into:

X＝S-(R+W _i+a)×K

In formula: a is the total amount (t) of the nitrogen phosphorus that aquaculture produces.

Compared with prior art, the present invention at least has following beneficial effect:

Conveniently can show that by adopting this model the nitrogen phosphorus of polluted bed mud in arealriver, lake is to water body contribution amount, calculate average annual burst size and the rate of release of bottom mud in lake nitrogen and phosphorus pollutants, thus achieve the macroanalysis that the total amount of pollutant in water body in lake is formed; The conclusion drawn by the method substantially meets objective law and the method application is convenient, can be widely used in the main pollution structure analysis in present stage lake.

Accompanying drawing explanation

Fig. 1 is the substrate sludge nitrogen phosphor contaminant burst size measuring principle schematic diagram in the present invention.

Fig. 2 is mud loam core, the mound seabed Isotope Dating matched curve in the embodiment of the present invention 1.

Embodiment

For ease of understanding the present invention, it is as follows that the present invention enumerates embodiment.Those skilled in the art should understand, described embodiment is only help to understand the present invention, should not be considered as concrete restriction of the present invention.

Embodiment 1

Nitrogen and phosphorus pollutants burst size in the mud of mound seabed is measured.

(1) base case:

Qiong Hai is positioned at south, Xichang City city east 5km, lake storage capacity 2.76 hundred million m ³, area of lake 27.4km ², average annual rainfall amount is 1004.2mm.In the body of lake, total nitrogen, total phosphorus mean concentration are 0.421mg/L and 0.017mg/L.

Bed mud genesis analysis, is divided into from top to bottom: alluvial sediment layer → clay seam/root system of plant layer → calcareous clay layer.Alluvial sediment layer black, mould shape in stream-like-stream, containing corruption blackening plant residue, have putrefactive odor.Alluvial sediment layer is the main presence of pollution sources in lake, is the zone of interest of environmental dredging; The color of clay seam is grey, containing containing canebreak on a small quantity or not, is the geology substrate that lake is formed.

Bed mud horizontal distribution, section, northwest is owing to Haihe River in history back-silting, and be the most serious region of full lake alluvial, bed mud is black or reddish black, and lakebed does not have aquatic vegetation substantially; Section, north is due to reasons such as soil erosions, and local sedimentation is serious, and sediment particles is comparatively thick, in reddish black, has obvious organic composition, by the content of nitrogen and phosphorous higher than regional background value; Section, middle part silt depth is relatively little, and particle is thin, takes on a red color or reddish black, and lakebed has aquatic vegetation in blocks to exist.

The present embodiment has carried out stratified sampling in the middle of a lake to bed mud, and utilizes ²¹⁰pb and ¹³⁷the method of Cs isotope tracling method, determines the rate of sedimentation of bed mud.Calculate according to ingoing river flow and average annual pollutant levels, total nitrogen enters lake amount 97t every year, goes out lake amount every year for 25.2t; Total phosphorus enters lake amount 10.1t every year, goes out lake amount every year for 3.44t; Degradation coefficient temperature influence alters a great deal, and Various Seasonal lake water temperature has notable difference, gets K=K ₂₀* 1.047T-20, the achievement in research with reference to Poyang Lake Danjiangkou Reservoir, reservoir area of Three Gorges and Hanyang Si Hu carries out the calibration of numerical model parameter with the data of water quality monitoring of 2000 ~ 2005, determine accumulation degradation coefficient K _20TN=0.008d ^-1, k _20TP=0.05d ^-1.

(2) analysis on monitoring result

A) nitrogen phosphorus testing result

Nitrogen and phosphorus are the nutrients of plant growth, and when in bottom mud in lake, the content of nitrogen and phosphorous is high, sediment interstitial water has certain flow rate or under Interstitial Water concentration gradient, nitrogen and phosphorus can be discharged in lake water and form endogenous pollution.Total nitrogen content 0.24g/kg ~ 1.79g/kg in the mud of mound seabed, mean value: 1257mg/kg; Total phosphorus content 0.17g/kg ~ 0.63g/kg, mean value: 532mg/kg.

B) Isotope Dating

The age in mud loam core, mound seabed uses ²¹⁰pb and ¹³⁷cs Isotopic Dating is determined.In sediment ²¹⁰pb, from two parts, a part be by ²²⁶ra decay also reaches with it mobile equilibrium ²¹⁰pb, a part is from the precipitum in air and the surplus that constantly decays of concentration ²¹⁰pb (is denoted as ²¹⁰pbex).In the present embodiment ²¹⁰pb adopts constant recharge rate pattern (CRSmodel) to calculate, and Fig. 1 shows the matched curve of mud loam core, mound seabed Isotope Dating.

Deposited the corresponding relation in time by the CRS model calculating acquisition bed mud degree of depth and bed mud, and shown by bed mud Isotope Dating result, this region bed mud rate of sedimentation is very fast, and bed mud average year rate of sedimentation reaches 3.06cm/a.Other Inner Mongols, lake of analogy Ulansuhai Nur 0.47cm/a is (see Zhao Suozhi etc., Inner Mongol Ulansuhai Nur lake water and bed mud nutrient and heavy metal pollution and environmental effect research thereof, Beijing: The Chinese Geology Univ. (Beijing), 1-97 page, 2013), Lake Fuxian, Yunnan Province 0.02cm/a (see Wang little Di etc., utilizes ²¹⁰pb, ¹³⁷cs, ²⁴¹am counts year method research Lake Fuxian, Yunnan Province Recent Sedimentation Rates, lake science, the 22nd volume the 1st phase, 136-142 page, 2010), Qinghai Lake 0.020cm/a (see Zhang Xinbao etc., ¹³⁷the trial of Cs mass balance approach measuring and calculating Qinghai Lake Recent Sedimentation Rates, lake science, the 21st volume the 6th phase, 827-833 page, 2009) known, mound seabed mud rate of sedimentation is fast, has much relations with the severe water and soil erosion in this basin.

(3) mound sea Nitrogen In Sediment Phosphurus release amount result of calculation

Nitrogen Phosphurus release amount is utilized to account model: (I) conclusion is calculated: mound seabed mud total nitrogen annual efflux is about 243.63t, and average rate of release is 24.3mg/ (m ²d); Total phosphorus annual efflux is about 93.28t, and average rate of release is 9.3mg/ (m ²d), the nitrogen phosphorus amount calculating bed mud contribution in the body of Qiong Hai lake according to the degradation rate of pollutant is respectively 94.19t and 4.76t, accounts for lake body nitrogen respectively, phosphorus contributes 40% and 48% of total amount.

(4) analogy method is adopted to prove the rationality that nitrogen Phosphurus release amount accounts model

In current prior art, Nitrogen In Sediment phosphorus dissolution rate is respectively at 1mg/ (m ²d) ~ 300mg/ (m ²d) with 0.2mg/ (m ²d) ~ 100mg/ (m ²d) in scope (see the bright chief editor of metallographic, lake eutrophication control and administrative skill, Beijing: Chemical Industry Press, 1-6 page, calendar year 2001); The average rate of release of nitrogen under not disturbance and disturbed conditions is respectively 56mg/ (m ²d) with 95mg/ (m ²d) (see Lin Jianwei etc., watercourse aeration on the impact of eutrophic water sedimentary nitrogen Phosphurus release, ecologic environment, the 14th volume the 6th phase, 812-815 page, 2005 years); Phosphorus is 2.85mg/ (m under aerobic condition ²d) ~ 5.71mg/ (m ²d); Be 1.43mg/ (m under anaerobic condition ²d) ~ 14.29mg/ (m ²d) (see Lee-HyungK, et.al.Phosphorusreleaseratesfromsedimentsandpollutantcha racteristicsinHanRiver, Seoul, Korea, ScienceofTheTotalEnvironment, (321): 115-125,2004); In neutral conditions, the rate of release of total nitrogen is 33.08mg/ (m ²d), be 53.56mg/ (m under acid condition ²d), be 57.11mg/ (m in the basic conditions ²d) (see Liang Shuxuan etc., the impact of pH value dialogue ocean deposit thing nitrogen Phosphurus release, Agriculture of Anhui science, the 38th volume the 36th phase, 20859-20862 page, 2010 years).It is 3.49mg/ (m that domestic existing achievement in research on average releases phosphorus amount as the West Lake ²d) (see Wu Genfu etc., sediment of West Lake, Hangzhou releases the Primary Study of phosphorus, China Environmental Science, the 18th volume the 2nd phase, 107-110 page, 1998), the phosphorus that its lake, North can be disengaged for 1 year is about 7.22t, is equivalent to external source and enters 2 times of phosphorus amount and (edit see Wu Jingbo, Chinese Lakes eutrophication, Beijing: China Environmental Science Press, 442-447 page, nineteen ninety); Ulansuhai Nur year stripping quantity total nitrogen 280t, total phosphorus 50t, be equivalent to exogenous nitrogen, phosphorus input quantity 25% and 83% (see Zhao Suozhi, Inner Mongol Ulansuhai Nur lake water and bed mud nutrient and heavy metal pollution and environmental effect research thereof, Beijing: The Chinese Geology Univ. (Beijing), 1-97 page, 2013).Comprehensive above research conclusion, the zone of reasonableness of the average rate of release of Nitrogen In Sediment, phosphorus should be respectively at 20 ~ 100mg/ (m ²d) He 1 ~ 15mg/ (m ²d), within, tentatively can judge that this research calculated results is within zone of reasonableness thus.

Can be found out by above embodiment, adopt nitrogen Phosphurus release amount of the present invention to account model and conveniently can show that the nitrogen phosphorus of polluted bed mud in arealriver, lake is to water body contribution amount.Because nitrogen, phosphorus play a crucial role in body eutrophication process, rate of release and the burst size of Nitrogen In Sediment phosphorus have material impact to body eutrophication, therefore by this nitrogen Phosphurus release amount account model can realize in water body in lake the total amount of pollutant form macroanalysis, and effectively reflect the main pollution structure in present stage lake, there is important using value.

Applicant states; the foregoing is only the specific embodiment of the present invention; but protection scope of the present invention is not limited thereto; person of ordinary skill in the field should understand; anyly belong to those skilled in the art in the technical scope that the present invention discloses; the change that can expect easily or replacement, all drop within protection scope of the present invention and open scope.

Claims (7)

1. an assay method for Nitrogen In Sediment phosphor contaminant burst size, is characterized in that, said method comprising the steps of:

(1) adopt the annual average water volume of flowmeter to river, lake of coming in and going out to measure, and adopt digest by potassium persulfate to measure pollutant total phosphorus concentration and adopt alkaline chitinase to clear up determined by ultraviolet spectrophotometry pollutant total nitrogen concentration to determine the average annual inlet W of pollutant rainwash _iquantum of output W average annual with pollutant rainwash _o;

(2) average annual rainfall volume R is determined to the average annual rainfall amount analysis in basin, place, river, lake;

(3) stratified sampling and Isotope Dating are carried out to determine the average annual hold-up S of pollutant in river, lake and bed mud deposition total amount P to lake bed mud in river, and draw the accumulation degradation coefficient K of pollutant;

(4) the total amount a of the nitrogen phosphorus that aquaculture produces is calculated;

(5) the average annual burst size of Nitrogen In Sediment phosphor contaminant is calculated according to formula (I) or formula (II):

$X=\frac{W_o+S+P}{1-K}-W_i-R---\left(I\right)$

X＝S-(R+W _i+a)×K(II)

Wherein, X is sediment pollution annual efflux (t); W _ifor the average annual inlet (t) of pollutant rainwash; W _ofor the average annual quantum of output (t) of pollutant rainwash; R is average annual rainfall volume (t); S is the average annual hold-up (t) of pollutant; P is bed mud deposition total amount (t); K is the degradation coefficient of pollutant; A is the total amount (t) of the nitrogen phosphorus that aquaculture produces.

2. assay method according to claim 1, is characterized in that, the described average annual rainfall volume R of step (2) calculates according to formula (III):

R＝n·r·S·C _R·10 ^-3(III)

Wherein, n is polluted bed mud deposition year number (a); R is average annual rainfall amount (mm); S is the average annual hold-up (t) of pollutant; C _rfor pollutant levels in the rain.

3. assay method according to claim 1 and 2, is characterized in that, the average annual hold-up S of step (3) described pollutant calculates according to formula (IV):

$S={\stackrel{\‾}{C}}_w\·Q\×100---\left(IV\right)$

Wherein, for pollutant mean annual concentration (mg/L) in water body; Q is the volume or storage capacity (hundred million m that calculate water body ³).

4. the assay method according to any one of claim 1-3, is characterized in that, step (3) described bed mud deposition total amount P calculates according to formula (V):

$P=C_p\·s\·h\·(1-\mathrm{\φ})\·\frac{\mathrm{\ρ}}{n}---\left(V\right)$

Wherein, C _pfor pollutants in sediments mean concentration (mg/kg); S is the bed mud area (km of whole water body ²); H is the polluted bed mud degree of depth (m); φ is water cut (%); ρ is bed mud unit dry weight (g/cm ³); N is polluted bed mud deposition year number (a).

5. the assay method according to any one of claim 1-4, is characterized in that, the described accumulation degradation coefficient K of step (4) calculates according to formula (VI):

K＝exp(-k′Δt)(VI)

Wherein, K is accumulation degradation coefficient (nd ^-1); K ' is day degradation coefficient (d ^-1); Δ t is the sedimentation time that Isotope Dating draws, identical with bed mud sedimentation time.

6. the assay method according to any one of claim 1-5, is characterized in that, described Isotope Dating is ²¹⁰pb determine year or ¹³⁷cs determines year.

7. assay method according to claim 6, is characterized in that, described in ²¹⁰pb determines to adopt constant recharge rate mode computation average sedimentation rate year.