Internal loading potential of phosphorus in reservoirs along a semiarid watershed

Moura, Diana Souza; Almeida, Antonia Samylla Oliveira De; Pestana, Carlos João; Girão, Laura Gomes; Capelo-Neto, José

doi:10.1590/2318-0331.252020180023

Acessibilidade / Reportar erro

Brasil

Español English

sumário « anterior atual seguinte »

Sumário

Scientific/Technical Article • RBRH 25 • 2020 • https://doi.org/10.1590/2318-0331.252020180023 copy

Internal loading potential of phosphorus in reservoirs along a semiarid watershed

Potencial de recarga interna de fósforo em reservatórios ao longo de uma bacia hidrográfica no semiárido

Authorship SCIMAGO INSTITUTIONS RANKINGS

ABSTRACT

Sediments are important to nutrient dynamics, especially due to phosphorus internal loading. Several studies have observed that internal loading could prevent water quality from improving in lakes, even when external phosphorus loading is significantly decreased. Therefore, there is an urgent need to assess the potential release of phosphorus contained in the sediment, and thus, its potential to impact water quality. In this study, the vertical and horizontal distributions of distinct phosphorus forms in the bottom sediments of artificial reservoirs, located at Forquilha watershed (Ceará, Brazil), were investigated through sequential chemical fractionation. The reservoirs Lagoa Cercada (R#1), Riacho do Algodão (R#2), Riacho Verde (R#3), Cachoeira (R#4), Chagas Manu (R#5), Quandu (R#6) and Balanças (R#7) were investigated. Reservoirs R#1 (most downstream reservoir of the watershed) and R#7 (most upstream reservoir of the watershed) had higher concentrations of total phosphorus (P_T) and lower pH values, potentially exerting greater influence in phosphorus concentration in the water column. Reservoirs R#3 and R#4 presented a predominance of residual phosphorus (P_Re), the least available fractions of phosphorus and thus, presented a lower potential for internal loading. Reservoirs R#5, R#1 and R#2 showed a tendency of decreasing total phosphorus (P_T) as the sediment depth increased, probably indicating an increase of allochthonous phosphorus loading along time. Reservoir R#6 showed the predominance of P_FeAl and P_Ca fractions on points A and B, respectively, showing that the characteristics of the sediments may vary in the same reservoir. Mobile (P_M) and iron and aluminum-bound phosphorus (P_FeAl) were the least and the most abundant fractions in most of the samples analyzed, respectively.

Keywords:
Water quality; Bottom sediment; Phosphorus availability; Eutrophication potential

1st Sampling campaign
Reservoir	Points	Maximum Depth (cm)	Zone	Subsamples
R#1 – Lagoa Cercada	A	59	Lacustrine	13
R#1 – Lagoa Cercada	B	23	Transitional	13
R#2 – Riacho do Algodão	A	12	Lacustrine	6
	B	4	Transitional	2
	C	7	Riverine	2
R#3 – Riacho Verde	A	11	Lacustrine	5
	B	19	Transitional	5
	C	17	Riverine	5
2nd Sampling campaign
R#4 - Cachoeira	A	11	Lacustrine	4
R#4 - Cachoeira	B	5	Transitional	2
R#5 – Chagas Manu	A	5	Lacustrine	2
R#5 – Chagas Manu	B	5	Transitional	2
R#6 - Quandu	A	39	Lacustrine	11
R#6 - Quandu	B	46	Lacustrine	7
R#7 - Balanças	A	15	Lacustrine	3

Reservoir	Point		pH
Reservoir	Point	Average	SD	CV (%)
R#1	A	4.8	0.5	11
R#1	B	5.6	0.6	11
R#2	A	6.2	0.9	15
	B	5.5	0.6	11
	C	6,1	0.2	10
R#3	A	7.0	0.5	7
	B	6.9	0.4	6
	C	6.1	0.8	13
R#4	A	6.5	0.1	1
R#4	B	6.5	0.3	4
R#5	A	7.1	0.1	1
R#5	B	7.0	0.3	4
R#6	A	6.1	0.2	3
R#6	B	6.1	0.1	2
R#7	A	6.1	0.1	2

Reservoir	Situation	Age (years)	Point	Predominant	PO	PI	PT
Reservoir	Situation	Age (years)	Point	fraction of PI (% PT)	(% PT)	(% PT)	(mg.kg^-1)
R#1	Dry	20	A	P_FeAl - 58%	0	100%	940.1
R#1	Dry	20	B	P_FeAl - 37%	39%	61%	677.6
R#2	Wet	12	A	P_FeAl - 15%	57%	43%	499.9
			B	P_FeAl - 20%	58%	42%	618.6
			C	P_FeAl - 14%	67%	33%	467.7
R#3	Wet	17	A	P_Ca- 33%	30%	70%	524.0
			B	P_Ca - 22%	47%	53%	446.8
			C	P_FeAl -12%	64%	36%	560.4
			C	P_Ca - 12%	64%	36%	560.4
R#4	Wet	3	A	P_Re - 73%	9%	91%	396.3
R#4	Wet	3	B	P_Re - 71%	5%	95%	398.1
R#5	Wet	2	A	P_FeAl - 12%	63%	37%	551.6
			A	P_Re - 12%	63%	37%	551.6
			B	P_Re - 50%	25%	75%	658.9
R#6	Dry	8	A	P_FeAl - 22%	52%	48%	772.5
R#6	Dry	8	B	P_Ca - 61%	3%	97%	694.2
R#7	Dry	8	A	P_FeAl - 23%	51%	49%	815.5

Associação Brasileira de Recursos Hídricos Av. Bento Gonçalves, 9500, CEP: 91501-970, Tel: (51) 3493 2233, Fax: (51) 3308 6652 - Porto Alegre - RS - Brazil
E-mail: rbrh@abrh.org.br

Acompanhe os números deste periódico no seu leitor de RSS

[1] E-mails: dianasm_@hotmail.com (DSM), samylla_17@hotmail.com (ASOA), c.pestana1@rgu.ac.uk (CJP), laura_gomesgirao@hotmail.com (LGG), capelo@ufc.br (JCN).